Add UWP targets

i686 support doesn't compile yet, but x86_64 does, and resulting
cdylib's are passing the WACK tests

src/librustc_target/spec/i686_pc_uwp_gnu.rs

@@ -0,0 +1,27 @@
+use crate::spec::{LinkerFlavor, Target, TargetResult};
+
+pub fn target() -> TargetResult {
+    let mut base = super::uwp_base::opts();
+    base.cpu = "pentium4".to_string();
+    base.max_atomic_width = Some(64);
+    base.eliminate_frame_pointer = false; // Required for backtraces
+
+    // Mark all dynamic libraries and executables as compatible with the larger 4GiB address
+    // space available to x86 Windows binaries on x86_64.
+    base.pre_link_args
+        .get_mut(&LinkerFlavor::Gcc).unwrap().push("-Wl,--large-address-aware".to_string());
+
+    Ok(Target {
+        llvm_target: "i686-pc-windows-gnu".to_string(),
+        target_endian: "little".to_string(),
+        target_pointer_width: "32".to_string(),
+        target_c_int_width: "32".to_string(),
+        data_layout: "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32".to_string(),
+        arch: "x86".to_string(),
+        target_os: "uwp".to_string(),
+        target_env: "gnu".to_string(),
+        target_vendor: "pc".to_string(),
+        linker_flavor: LinkerFlavor::Gcc,
+        options: base,
+    })
+}

src/librustc_target/spec/mod.rs

@@ -61,6 +61,7 @@ mod solaris_base;
 mod uefi_base;
 mod windows_base;
 mod windows_msvc_base;
+mod uwp_base;
 mod thumb_base;
 mod l4re_base;
 mod fuchsia_base;
@@ -434,6 +435,8 @@ supported_targets! {
 
     ("x86_64-pc-windows-gnu", x86_64_pc_windows_gnu),
     ("i686-pc-windows-gnu", i686_pc_windows_gnu),
+    ("i686-pc-uwp-gnu", i686_pc_uwp_gnu),
+    ("x86_64-pc-uwp-gnu", x86_64_pc_uwp_gnu),
 
     ("aarch64-pc-windows-msvc", aarch64_pc_windows_msvc),
     ("x86_64-pc-windows-msvc", x86_64_pc_windows_msvc),

src/librustc_target/spec/uwp_base.rs

@@ -0,0 +1,69 @@
+use crate::spec::{LinkArgs, LinkerFlavor, TargetOptions};
+use std::default::Default;
+
+pub fn opts() -> TargetOptions {
+    let mut pre_link_args = LinkArgs::new();
+    pre_link_args.insert(LinkerFlavor::Gcc, vec![
+            // Tell GCC to avoid linker plugins, because we are not bundling
+            // them with Windows installer, and Rust does its own LTO anyways.
+            "-fno-use-linker-plugin".to_string(),
+
+            // Always enable DEP (NX bit) when it is available
+            "-Wl,--nxcompat".to_string(),
+
+            // Do not use the standard system startup files or libraries when linking
+            "-nostdlib".to_string(),
+        ]);
+
+    let mut late_link_args = LinkArgs::new();
+    late_link_args.insert(LinkerFlavor::Gcc, vec![
+        //"-lwinstorecompat".to_string(),
+        //"-lmingwex".to_string(),
+        //"-lwinstorecompat".to_string(),
+        "-lwinstorecompat".to_string(),
+        "-lruntimeobject".to_string(),
+        "-lsynchronization".to_string(),
+        "-lvcruntime140_app".to_string(),
+        "-lucrt".to_string(),
+        "-lwindowsapp".to_string(),
+        "-lmingwex".to_string(),
+        "-lmingw32".to_string(),
+    ]);
+
+    TargetOptions {
+        // FIXME(#13846) this should be enabled for windows
+        function_sections: false,
+        linker: Some("gcc".to_string()),
+        dynamic_linking: true,
+        executables: false,
+        dll_prefix: String::new(),
+        dll_suffix: ".dll".to_string(),
+        exe_suffix: ".exe".to_string(),
+        staticlib_prefix: "lib".to_string(),
+        staticlib_suffix: ".a".to_string(),
+        no_default_libraries: true,
+        target_family: Some("windows".to_string()),
+        is_like_windows: true,
+        allows_weak_linkage: false,
+        pre_link_args,
+        pre_link_objects_exe: vec![
+            "crt2.o".to_string(),    // mingw C runtime initialization for executables
+            "rsbegin.o".to_string(), // Rust compiler runtime initialization, see rsbegin.rs
+        ],
+        pre_link_objects_dll: vec![
+            "dllcrt2.o".to_string(), // mingw C runtime initialization for dlls
+            "rsbegin.o".to_string(),
+        ],
+        late_link_args,
+        post_link_objects: vec![
+            "rsend.o".to_string(),
+            "libgcc.a".to_string(), // libgcc or compiler-rt
+        ],
+        custom_unwind_resume: true,
+        abi_return_struct_as_int: true,
+        emit_debug_gdb_scripts: false,
+        requires_uwtable: true,
+
+        .. Default::default()
+    }
+}

src/librustc_target/spec/x86_64_pc_uwp_gnu.rs

@@ -0,0 +1,22 @@
+use crate::spec::{LinkerFlavor, Target, TargetResult};
+
+pub fn target() -> TargetResult {
+    let mut base = super::uwp_base::opts();
+    base.cpu = "x86-64".to_string();
+    base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
+    base.max_atomic_width = Some(64);
+
+    Ok(Target {
+        llvm_target: "x86_64-pc-windows-gnu".to_string(),
+        target_endian: "little".to_string(),
+        target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
+        data_layout: "e-m:w-i64:64-f80:128-n8:16:32:64-S128".to_string(),
+        arch: "x86_64".to_string(),
+        target_os: "uwp".to_string(),
+        target_env: "gnu".to_string(),
+        target_vendor: "pc".to_string(),
+        linker_flavor: LinkerFlavor::Gcc,
+        options: base,
+    })
+}