[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 `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `clang,llvm` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/14277

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

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: CodeGen/Mips/subtarget-feature-test.c' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
z:\b\llvm-clang-x86_64-sie-win\build\bin\clang.exe --target=mips64-linux-gnu -mcpu=i6400 -o Z:\b\llvm-clang-x86_64-sie-win\build\tools\clang\test\CodeGen\Mips\Output\subtarget-feature-test.c.tmp -c Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\CodeGen\Mips\subtarget-feature-test.c 2>&1 | z:\b\llvm-clang-x86_64-sie-win\build\bin\filecheck.exe --allow-empty Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\CodeGen\Mips\subtarget-feature-test.c
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\clang.exe' --target=mips64-linux-gnu -mcpu=i6400 -o 'Z:\b\llvm-clang-x86_64-sie-win\build\tools\clang\test\CodeGen\Mips\Output\subtarget-feature-test.c.tmp' -c 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\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: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\filecheck.exe' --allow-empty 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\CodeGen\Mips\subtarget-feature-test.c'

--

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


```

</details>

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