Auto merge of #135074 - wzssyqa:mips-mti, r=oli-obk

Target: Add mips mti baremetal support

Do the same thing as gcc, which use the vendor `mti` to mark the toolchain as MIPS32r2 default.

We support both big endian and little endian flavor:
  mips-mti-none-elf
  mipsel-mti-none-elf

src/doc/rustc/src/SUMMARY.md

@@ -62,6 +62,7 @@
     - [m68k-unknown-linux-gnu](platform-support/m68k-unknown-linux-gnu.md)
     - [mips64-openwrt-linux-musl](platform-support/mips64-openwrt-linux-musl.md)
     - [mipsel-sony-psx](platform-support/mipsel-sony-psx.md)
+    - [mips\*-mti-none-elf](platform-support/mips-mti-none-elf.md)
     - [mipsisa\*r6\*-unknown-linux-gnu\*](platform-support/mips-release-6.md)
     - [nvptx64-nvidia-cuda](platform-support/nvptx64-nvidia-cuda.md)
     - [powerpc-unknown-openbsd](platform-support/powerpc-unknown-openbsd.md)

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

@@ -332,6 +332,8 @@ target | std | host | notes
 `mipsel-unknown-linux-uclibc` | ✓ |  | MIPS (LE) Linux with uClibc
 [`mipsel-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | 32-bit MIPS (LE), requires mips32 cpu support
 `mipsel-unknown-none` | * |  | Bare MIPS (LE) softfloat
+[`mips-mti-none-elf`](platform-support/mips-mti-none-elf.md) | * |  | Bare MIPS32r2 (BE) softfloat
+[`mipsel-mti-none-elf`](platform-support/mips-mti-none-elf.md) | * |  | Bare MIPS32r2 (LE) softfloat
 [`mipsisa32r6-unknown-linux-gnu`](platform-support/mips-release-6.md) | ? |  | 32-bit MIPS Release 6 Big Endian
 [`mipsisa32r6el-unknown-linux-gnu`](platform-support/mips-release-6.md) | ? |  | 32-bit MIPS Release 6 Little Endian
 [`mipsisa64r6-unknown-linux-gnuabi64`](platform-support/mips-release-6.md) | ? |  | 64-bit MIPS Release 6 Big Endian

src/doc/rustc/src/platform-support/mips-mti-none-elf.md

@@ -0,0 +1,31 @@
+# `mips*-mti-none-elf`
+
+**Tier: 3**
+
+MIPS32r2 baremetal softfloat, Big Endian or Little Endian.
+
+- mips-mti-none-elf
+- mipsel-mti-none-elf
+
+## Target maintainers
+
+- YunQiang Su, `syq@debian.org`, https://github.com/wzssyqa
+
+## Background
+
+These 2 targets, aka mips-mti-none-elf and mipsel-mti-none-elf, are for
+baremetal development of MIPS32r2. The lld is used instead of Gnu-ld.
+
+## Requirements
+
+The target only supports cross compilation and no host tools. The target
+supports `alloc` with a default allocator while only support `no-std` development.
+
+The vendor name `mti` follows the naming of gcc to indicate MIPS32r2.
+
+## Cross-compilation toolchains and C code
+
+Compatible C code can be built for this target on any compiler that has a MIPS32r2
+target.  On clang and ld.lld linker, it can be generated using the
+`-march=mips`/`-march=mipsel`, `-mabi=32` with llvm features flag
+`features=+mips32r2,+soft-float,+noabicalls`.

src/tools/build-manifest/src/main.rs

@@ -128,6 +128,8 @@ static TARGETS: &[&str] = &[
     "mipsisa64r6el-unknown-linux-gnuabi64",
     "mipsel-unknown-linux-gnu",
     "mipsel-unknown-linux-musl",
+    "mips-mti-none-elf",
+    "mipsel-mti-none-elf",
     "nvptx64-nvidia-cuda",
     "powerpc-unknown-linux-gnu",
     "powerpc64-unknown-linux-gnu",