[clang] [llvm] [MIPS] Define SubTargetFeature for i6500 cpu (PR #132907)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-cmake-x86_64-avx512-win` running on `avx512-intel64-win` while building `clang,llvm` at step 6 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/81/builds/5698

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: CodeGen/Mips/subtarget-feature-test.c' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
d:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\bin\clang.exe --target=mips64-linux-gnu -mcpu=i6400 -o D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\tools\clang\test\CodeGen\Mips\Output\subtarget-feature-test.c.tmp -c D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\clang\test\CodeGen\Mips\subtarget-feature-test.c 2>&1 | d:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\bin\filecheck.exe --allow-empty D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\clang\test\CodeGen\Mips\subtarget-feature-test.c
# executed command: 'd:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\bin\clang.exe' --target=mips64-linux-gnu -mcpu=i6400 -o 'D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\tools\clang\test\CodeGen\Mips\Output\subtarget-feature-test.c.tmp' -c 'D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\clang\test\CodeGen\Mips\subtarget-feature-test.c'
# note: command had no output on stdout or stderr
# error: command failed with exit status: 1
# executed command: 'd:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\stage1\bin\filecheck.exe' --allow-empty 'D:\buildbot\llvm-worker\clang-cmake-x86_64-avx512-win\llvm\clang\test\CodeGen\Mips\subtarget-feature-test.c'

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/132907