[llvm-branch-commits] [compiler-rt] Build libfuzzer sources with the chosen C++ compiler (PR #83090)

[Alexander Richardson via llvm-branch-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/83090

I was getting build failures due to missing <cstddef> when building the
libfuzzer tests. It turns out that the custom command was using
COMPILER_RT_TEST_COMPILER when building the source file rather than
the COMPILER_RT_TEST_CXX_COMPILER.