[clang] [Clang] Improve infrastructure for libstdc++ workarounds (PR #141977)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `clang` at step 11 "ninja check 2".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/10091

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

```
Step 11 (ninja check 2) failure: stage 2 checked (failure)
******************** TEST 'Clang :: SemaCXX/libstdcxx_pair_swap_hack.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/bin/clang -cc1 -internal-isystem /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/lib/clang/21/include -nostdsysteminc -fsyntax-only /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array # RUN: at line 10
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/bin/clang -cc1 -internal-isystem /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/stage2/lib/clang/21/include -nostdsysteminc -fsyntax-only /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp -std=c++11 -verify -fexceptions -fcxx-exceptions -D__GLIBCXX__=20100000L -DCLASS=array
error: 'expected-error' diagnostics seen but not expected: 
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: exception specification of 'swap' uses itself
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: too many arguments to function call, expected single argument 'other', have 2 arguments
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: exception specification of 'swap' uses itself
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: too many arguments to function call, expected single argument 'other', have 2 arguments
error: 'expected-note' diagnostics seen but not expected: 
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 78: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 78: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: 'swap' declared here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 79: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 79: in instantiation of exception specification for 'swap' requested here
  File /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-multistage-test/clang-ppc64le-multistage/llvm/clang/test/SemaCXX/libstdcxx_pair_swap_hack.cpp Line 51: 'swap' declared here
12 errors generated.

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/141977