Provide prebuilt std for gnullvm targets

src/ci/docker/host-x86_64/dist-various-1/Dockerfile

@@ -55,6 +55,9 @@ RUN ./install-riscv64-none-elf.sh
 COPY host-x86_64/dist-various-1/install-riscv32-none-elf.sh /build
 RUN ./install-riscv32-none-elf.sh
 
+COPY host-x86_64/dist-various-1/install-llvm-mingw.sh /build
+RUN ./install-llvm-mingw.sh
+
 # Suppress some warnings in the openwrt toolchains we downloaded
 ENV STAGING_DIR=/tmp
 
@@ -111,6 +114,9 @@ ENV TARGETS=$TARGETS,armv7r-none-eabi
 ENV TARGETS=$TARGETS,armv7r-none-eabihf
 ENV TARGETS=$TARGETS,thumbv7neon-unknown-linux-gnueabihf
 ENV TARGETS=$TARGETS,armv7a-none-eabi
+ENV TARGETS=$TARGETS,aarch64-pc-windows-gnullvm
+ENV TARGETS=$TARGETS,i686-pc-windows-gnullvm
+ENV TARGETS=$TARGETS,x86_64-pc-windows-gnullvm
 
 ENV CFLAGS_armv5te_unknown_linux_musleabi="-march=armv5te -marm -mfloat-abi=soft" \
     CFLAGS_arm_unknown_linux_musleabi="-march=armv6 -marm" \
@@ -142,7 +148,10 @@ ENV CFLAGS_armv5te_unknown_linux_musleabi="-march=armv5te -marm -mfloat-abi=soft
     CC_riscv64imac_unknown_none_elf=riscv64-unknown-elf-gcc \
     CFLAGS_riscv64imac_unknown_none_elf=-march=rv64imac -mabi=lp64 \
     CC_riscv64gc_unknown_none_elf=riscv64-unknown-elf-gcc \
-    CFLAGS_riscv64gc_unknown_none_elf=-march=rv64gc -mabi=lp64
+    CFLAGS_riscv64gc_unknown_none_elf=-march=rv64gc -mabi=lp64 \
+    CC_aarch64_pc_windows_gnullvm=aarch64-w64-mingw32-clang \
+    CC_i686_pc_windows_gnullvm=i686-w64-mingw32-clang \
+    CC_x86_64_pc_windows_gnullvm=x86_64-w64-mingw32-clang
 
 ENV RUST_CONFIGURE_ARGS \
       --musl-root-armv5te=/musl-armv5te \

src/ci/docker/host-x86_64/dist-various-1/install-llvm-mingw.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -ex
+
+release_date=20240404
+archive=llvm-mingw-${release_date}-ucrt-ubuntu-20.04-x86_64.tar.xz
+curl -L https://github.com/mstorsjo/llvm-mingw/releases/download/${release_date}/${archive} | \
+tar --extract --lzma --strip 1 --directory /usr/local

src/doc/rustc/src/platform-support.md

@@ -138,6 +138,7 @@ target | std | notes
 `aarch64-fuchsia` | ✓ | Alias for `aarch64-unknown-fuchsia`
 [`aarch64-unknown-fuchsia`](platform-support/fuchsia.md) | ✓ | ARM64 Fuchsia
 [`aarch64-linux-android`](platform-support/android.md) | ✓ | ARM64 Android
+[`aarch64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ARM64 MinGW (Windows 10+), LLVM ABI
 [`aarch64-unknown-linux-ohos`](platform-support/openharmony.md) | ✓ | ARM64 OpenHarmony
 `aarch64-unknown-none-softfloat` | * | Bare ARM64, softfloat
 `aarch64-unknown-none` | * | Bare ARM64, hardfloat
@@ -161,6 +162,7 @@ target | std | notes
 `i586-unknown-linux-gnu` | ✓ | 32-bit Linux w/o SSE (kernel 3.2, glibc 2.17) [^x86_32-floats-x87]
 `i586-unknown-linux-musl` | ✓ | 32-bit Linux w/o SSE, musl 1.2.3 [^x86_32-floats-x87]
 [`i686-linux-android`](platform-support/android.md) | ✓ | 32-bit x86 Android [^x86_32-floats-return-ABI]
+[`i686-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | 32-bit x86 MinGW (Windows 10+), LLVM ABI [^x86_32-floats-return-ABI]
 `i686-unknown-freebsd` | ✓ | 32-bit FreeBSD [^x86_32-floats-return-ABI]
 `i686-unknown-linux-musl` | ✓ | 32-bit Linux with musl 1.2.3 [^x86_32-floats-return-ABI]
 [`i686-unknown-uefi`](platform-support/unknown-uefi.md) | ? | 32-bit UEFI
@@ -196,6 +198,7 @@ target | std | notes
 [`x86_64-unknown-fuchsia`](platform-support/fuchsia.md) | ✓ | 64-bit x86 Fuchsia
 [`x86_64-linux-android`](platform-support/android.md) | ✓ | 64-bit x86 Android
 `x86_64-pc-solaris` | ✓ | 64-bit Solaris 11, illumos
+[`x86_64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | 64-bit x86 MinGW (Windows 10+), LLVM ABI
 `x86_64-unknown-linux-gnux32` | ✓ | 64-bit Linux (x32 ABI) (kernel 4.15, glibc 2.27)
 [`x86_64-unknown-linux-ohos`](platform-support/openharmony.md) | ✓ | x86_64 OpenHarmony
 [`x86_64-unknown-none`](platform-support/x86_64-unknown-none.md) | * | Freestanding/bare-metal x86_64, softfloat
@@ -247,7 +250,7 @@ target | std | host | notes
 [`aarch64-apple-visionos-sim`](platform-support/apple-visionos.md) | ✓ |  | ARM64 Apple visionOS Simulator
 [`aarch64-kmc-solid_asp3`](platform-support/kmc-solid.md) | ✓ |  | ARM64 SOLID with TOPPERS/ASP3
 [`aarch64-nintendo-switch-freestanding`](platform-support/aarch64-nintendo-switch-freestanding.md) | * |  | ARM64 Nintendo Switch, Horizon
-[`aarch64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
+[`aarch64-unknown-linux-ohos`](platform-support/openharmony.md) | ✓ |  | ARM64 OpenHarmony |
 [`aarch64-unknown-teeos`](platform-support/aarch64-unknown-teeos.md) | ? |  | ARM64 TEEOS |
 [`aarch64-unknown-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | ARM64 QNX Neutrino 7.1 RTOS |
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
@@ -294,7 +297,7 @@ target | std | host | notes
 [`i586-pc-nto-qnx700`](platform-support/nto-qnx.md) | * |  | 32-bit x86 QNX Neutrino 7.0 RTOS  [^x86_32-floats-return-ABI]
 [`i586-unknown-netbsd`](platform-support/netbsd.md) | ✓ |  | 32-bit x86, restricted to Pentium
 `i686-apple-darwin` | ✓ | ✓ | 32-bit macOS (10.12+, Sierra+) [^x86_32-floats-return-ABI]
-[`i686-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ | [^x86_32-floats-return-ABI]
+`i686-pc-windows-msvc` | * |  | 32-bit Windows XP support [^x86_32-floats-return-ABI]
 `i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku [^x86_32-floats-return-ABI]
 [`i686-unknown-hurd-gnu`](platform-support/hurd.md) | ✓ | ✓ | 32-bit GNU/Hurd [^x86_32-floats-return-ABI]
 [`i686-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | NetBSD/i386 with SSE2 [^x86_32-floats-return-ABI]
@@ -370,7 +373,6 @@ target | std | host | notes
 [`x86_64-apple-tvos`](platform-support/apple-tvos.md) | ? |  | x86 64-bit tvOS
 [`x86_64-apple-watchos-sim`](platform-support/apple-watchos.md) | ✓ |  | x86 64-bit Apple WatchOS simulator
 [`x86_64-pc-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | x86 64-bit QNX Neutrino 7.1 RTOS |
-[`x86_64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
 [`x86_64-unikraft-linux-musl`](platform-support/unikraft-linux-musl.md) | ✓ |   | 64-bit Unikraft with musl 1.2.3
 `x86_64-unknown-dragonfly` | ✓ | ✓ | 64-bit DragonFlyBSD
 `x86_64-unknown-haiku` | ✓ | ✓ | 64-bit Haiku

src/doc/rustc/src/platform-support/pc-windows-gnullvm.md

@@ -1,6 +1,6 @@
 # \*-pc-windows-gnullvm
 
-**Tier: 3**
+**Tier: 2 (without host tools)**
 
 Windows targets similar to `*-pc-windows-gnu` but using UCRT as the runtime and various LLVM tools/libraries instead of GCC/Binutils.
 
@@ -12,38 +12,52 @@ Target triples available so far:
 ## Target maintainers
 
 - [@mati865](https://github.com/mati865)
+- [@thomcc](https://github.com/thomcc)
 
 ## Requirements
 
-The easiest way to obtain these targets is cross-compilation but native build from `x86_64-pc-windows-gnu` is possible with few hacks which I don't recommend.
+The easiest way to obtain these targets is cross-compilation, but native build from `x86_64-pc-windows-gnu` is possible with few hacks which I don't recommend.
 Std support is expected to be on pair with `*-pc-windows-gnu`.
 
 Binaries for this target should be at least on pair with `*-pc-windows-gnu` in terms of requirements and functionality.
 
 Those targets follow Windows calling convention for `extern "C"`.
 
-Like with any other Windows target created binaries are in PE format.
+Like with any other Windows target, created binaries are in PE format.
 
 ## Building the target
 
-For cross-compilation I recommend using [llvm-mingw](https://github.com/mstorsjo/llvm-mingw) toolchain, one change that seems necessary beside configuring cross compilers is disabling experimental `m86k` target. Otherwise LLVM build fails with `multiple definition ...` errors.
-Native bootstrapping builds require rather fragile hacks until host artifacts are available so I won't describe them here.
+These targets can be easily cross-compiled
+using [llvm-mingw](https://github.com/mstorsjo/llvm-mingw) toolchain or [MSYS2 CLANG*](https://www.msys2.org/docs/environments/) environments.
+Just fill `[target.*]` sections for both build and resulting compiler and set installation prefix in `config.toml`.
+Then run `./x.py install`.
+In my case I had ran `./x.py install --host x86_64-pc-windows-gnullvm --target x86_64-pc-windows-gnullvm` inside MSYS2 MINGW64 shell
+so `x86_64-pc-windows-gnu` was my build toolchain.
+
+Native bootstrapping is doable in two ways:
+- cross-compile gnullvm host toolchain and use it as build toolchain for the next build,
+- copy libunwind libraries and rename them to mimic libgcc like here: https://github.com/msys2/MINGW-packages/blob/68e640756df2df6df6afa60f025e3f936e7b977c/mingw-w64-rust/PKGBUILD#L108-L109, stage0 compiler will be mostly broken but good enough to build the next stage.
+
+The second option might stop working anytime, so it's not recommended.
 
 ## Building Rust programs
 
-Rust does not yet ship pre-compiled artifacts for this target. To compile for
-this target, you will either need to build Rust with the target enabled (see
-"Building the target" above), or build your own copy of `core` by using
-`build-std` or similar.
+Rust does ship a pre-compiled std library for those targets.
+That means one can easily cross-compile for those targets from other hosts if C proper toolchain is installed.
+
+Alternatively full toolchain can be built as described in the previous section.
 
 ## Testing
 
 Created binaries work fine on Windows or Wine using native hardware. Testing AArch64 on x86_64 is problematic though and requires spending some time with QEMU.
-Once these targets bootstrap themselves on native hardware they should pass Rust testsuite.
+Most of x86_64 testsuite does pass when cross-compiling,
+with exception for `rustdoc` and `ui-fulldeps` that fail with and error regarding a missing library,
+they do pass in native builds though.
+The only failing test is std's `process::tests::test_proc_thread_attributes` for unknown reason.
 
 ## Cross-compilation toolchains and C code
 
-Compatible C code can be built with Clang's `aarch64-pc-windows-gnu`, `i686-pc-windows-gnullvm` and `x86_64-pc-windows-gnu` targets as long as LLVM based C toolchains are used.
+Compatible C code can be built with Clang's `aarch64-pc-windows-gnu`, `i686-pc-windows-gnullvm` and `x86_64-pc-windows-gnu` targets as long as LLVM-based C toolchains are used.
 Those include:
 - [llvm-mingw](https://github.com/mstorsjo/llvm-mingw)
 - [MSYS2 with CLANG* environment](https://www.msys2.org/docs/environments)