[clang] [llvm] Add macro to suppress -Wunnecessary-virtual-specifier (PR #139614)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-s390x-linux-multistage` running on `systemz-1` while building `clang,llvm` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/98/builds/1425

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

```
Step 4 (build stage 1) failure: 'ninja -j4' (failure)
[1/6104] Building CXX object lib/Demangle/CMakeFiles/LLVMDemangle.dir/Demangle.cpp.o
[2/6104] Building CXX object lib/Demangle/CMakeFiles/LLVMDemangle.dir/DLangDemangle.cpp.o
[3/6104] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/ABIBreak.cpp.o
[4/6104] Building CXX object lib/Demangle/CMakeFiles/LLVMDemangle.dir/RustDemangle.cpp.o
[5/6104] Building CXX object lib/Demangle/CMakeFiles/LLVMDemangle.dir/MicrosoftDemangleNodes.cpp.o
[6/6104] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/AMDGPUMetadata.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/AMDGPUMetadata.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/include -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/AMDGPUMetadata.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/AMDGPUMetadata.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/AMDGPUMetadata.cpp.o -c /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/AMDGPUMetadata.cpp
In file included from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/STLFunctionalExtras.h:19,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/StringRef.h:13,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/Support/AMDGPUMetadata.h:18,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/AMDGPUMetadata.cpp:15:
/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/Support/Compiler.h:719:40: error: missing binary operator before token "("
  719 | #if defined(__clang__) && __has_warning("-Wunnecessary-virtual-specifier")
      |                                        ^
[7/6104] Building CXX object lib/Demangle/CMakeFiles/LLVMDemangle.dir/MicrosoftDemangle.cpp.o
[8/6104] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/APFixedPoint.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/APFixedPoint.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/include -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/APFixedPoint.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/APFixedPoint.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/APFixedPoint.cpp.o -c /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/APFixedPoint.cpp
In file included from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/APInt.h:18,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/APSInt.h:18,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/APFixedPoint.h:19,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/APFixedPoint.cpp:14:
/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/Support/Compiler.h:719:40: error: missing binary operator before token "("
  719 | #if defined(__clang__) && __has_warning("-Wunnecessary-virtual-specifier")
      |                                        ^
[9/6104] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/stage1/include -I/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -UNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/APFloat.cpp.o -c /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/APFloat.cpp
In file included from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/APInt.h:18,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/ADT/APFloat.h:18,
                 from /home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/lib/Support/APFloat.cpp:14:
/home/uweigand/sandbox/buildbot/clang-s390x-linux-multistage/llvm/llvm/include/llvm/Support/Compiler.h:719:40: error: missing binary operator before token "("
  719 | #if defined(__clang__) && __has_warning("-Wunnecessary-virtual-specifier")
      |                                        ^
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/139614