[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-solaris11-sparcv9` running on `solaris11-sparcv9` while building `clang,llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/13/builds/6233

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: CodeGen/Mips/subtarget-feature-test.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/clang --target=mips64-linux-gnu -mcpu=i6400 -o /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/tools/clang/test/CodeGen/Mips/Output/subtarget-feature-test.c.tmp -c /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/CodeGen/Mips/subtarget-feature-test.c 2>&1 | /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/FileCheck --allow-empty /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/CodeGen/Mips/subtarget-feature-test.c # RUN: at line 1
+ /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/clang --target=mips64-linux-gnu -mcpu=i6400 -o /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/tools/clang/test/CodeGen/Mips/Output/subtarget-feature-test.c.tmp -c /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/CodeGen/Mips/subtarget-feature-test.c
+ /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/stage1/bin/FileCheck --allow-empty /opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/clang/test/CodeGen/Mips/subtarget-feature-test.c

--

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


```

</details>

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