Drop mips*-unknown-linux-musl* to tier 3

Also be more pedantic about spelling:
- LE? Is it "less than or equal to"? Say "little endian".
- We're Rust, not C, preserve the initial capital in "N64".
- "MUSL" doesn't stand for anything; Rich Felker spells it "musl".

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

@@ -151,10 +151,6 @@ target | std | notes
 `i686-unknown-freebsd` | ✓ | 32-bit FreeBSD
 `i686-unknown-linux-musl` | ✓ | 32-bit Linux with MUSL
 [`i686-unknown-uefi`](platform-support/unknown-uefi.md) | * | 32-bit UEFI
-`mips-unknown-linux-musl` | ✓ | MIPS Linux with MUSL
-`mips64-unknown-linux-muslabi64` | ✓ | MIPS64 Linux, n64 ABI, MUSL
-`mips64el-unknown-linux-muslabi64` | ✓ | MIPS64 (LE) Linux, n64 ABI, MUSL
-`mipsel-unknown-linux-musl` | ✓ | MIPS (LE) Linux with MUSL
 [`nvptx64-nvidia-cuda`](platform-support/nvptx64-nvidia-cuda.md) | * | --emit=asm generates PTX code that [runs on NVIDIA GPUs]
 `riscv32i-unknown-none-elf` | * | Bare RISC-V (RV32I ISA)
 `riscv32imac-unknown-none-elf` | * | Bare RISC-V (RV32IMAC ISA)
@@ -270,11 +266,15 @@ target | std | host | notes
 [`loongarch64-unknown-none-softfloat`](platform-support/loongarch-none.md) | * |  | LoongArch64 Bare-metal (LP64S ABI)
 [`m68k-unknown-linux-gnu`](platform-support/m68k-unknown-linux-gnu.md) | ? |  | Motorola 680x0 Linux
 `mips-unknown-linux-gnu` | ✓ | ✓ | MIPS Linux (kernel 4.4, glibc 2.23)
+`mips-unknown-linux-musl` | ✓ |  | MIPS Linux with musl libc
 `mips-unknown-linux-uclibc` | ✓ |  | MIPS Linux with uClibc
 [`mips64-openwrt-linux-musl`](platform-support/mips64-openwrt-linux-musl.md) | ? |  | MIPS64 for OpenWrt Linux MUSL
 `mips64-unknown-linux-gnuabi64` | ✓ | ✓ | MIPS64 Linux, N64 ABI (kernel 4.4, glibc 2.23)
+`mips64-unknown-linux-muslabi64` | ✓ |  | MIPS64 Linux, N64 ABI, musl libc
 `mips64el-unknown-linux-gnuabi64` | ✓ | ✓ | MIPS64 (little endian) Linux, N64 ABI (kernel 4.4, glibc 2.23)
+`mips64el-unknown-linux-muslabi64` | ✓ |  | MIPS64 (little endian) Linux, N64 ABI, musl libc
 `mipsel-unknown-linux-gnu` | ✓ | ✓ | MIPS (little endian) Linux (kernel 4.4, glibc 2.23)
+`mipsel-unknown-linux-musl` | ✓ |  | MIPS (little endian) Linux with musl libc
 `mipsel-sony-psp` | * |  | MIPS (LE) Sony PlayStation Portable (PSP)
 [`mipsel-sony-psx`](platform-support/mipsel-sony-psx.md) | * |  | MIPS (LE) Sony PlayStation 1 (PSX)
 `mipsel-unknown-linux-uclibc` | ✓ |  | MIPS (LE) Linux with uClibc