[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 `arc-builder` running on `arc-worker` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/13692

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: CodeGen/Mips/subtarget-feature-test.c' FAILED ********************
Exit Code: 1

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

--

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


```

</details>

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