[clang] [Sparc][clang] implement `va_arg` in the clang frontend (PR #214981)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-x86_64-debian-dylib` running on `gribozavr4` while building `clang` at step 7 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/60/builds/7533

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

```
Step 7 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM-Unit :: CodeGen/./CodeGenTests/64/174' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/b/1/llvm-x86_64-debian-dylib/build/unittests/CodeGen/./CodeGenTests-LLVM-Unit-1241775-64-174.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=174 GTEST_SHARD_INDEX=64 /b/1/llvm-x86_64-debian-dylib/build/unittests/CodeGen/./CodeGenTests
--

Note: This is test shard 65 of 174.
[==========] Running 2 tests from 2 test suites.
[----------] Global test environment set-up.
[----------] 1 test from GCMetadataTest
[ RUN      ] GCMetadataTest.Basic
[       OK ] GCMetadataTest.Basic (0 ms)
[----------] 1 test from GCMetadataTest (0 ms total)

[----------] 1 test from SelectionDAGCSETest
[ RUN      ] SelectionDAGCSETest.EHLabel

--
exit: -11
--
shard JSON output does not exist: /b/1/llvm-x86_64-debian-dylib/build/unittests/CodeGen/./CodeGenTests-LLVM-Unit-1241775-64-174.json
********************


```

</details>

https://github.com/llvm/llvm-project/pull/214981