[llvm] Workaround -Wglobal-constructor warning. (PR #94699)

[Eric Schweitz via llvm-commits]

schweitzpgi wrote:

Here's the evidence/snippage that the warning/error actually can be triggered in our environ.
```console
$ make
[  0%] Built target LLVMDemangle
[  0%] Built target LLVMSupportBlake3
Consolidate compiler generated dependencies of target LLVMSupport
[  0%] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/CodeGenCoverage.cpp.o
/home/eric/tpls/llvm/llvm/lib/Support/CodeGenCoverage.cpp:24:30: error: declaration requires a global destructor [-Werror,-Wglobal-constructors]
static sys::SmartMutex<true> OutputMutex;
                             ^
1 error generated.
make[2]: *** [lib/Support/CMakeFiles/LLVMSupport.dir/build.make:426: lib/Support/CMakeFiles/LLVMSupport.dir/CodeGenCoverage.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:20373: lib/Support/CMakeFiles/LLVMSupport.dir/all] Error 2
make: *** [Makefile:156: all] Error 2
```


https://github.com/llvm/llvm-project/pull/94699