[NFC] [Support] Fix warning when build with clang-cl on Windows. (#65387)

Add const qualifier to avoid warning "_cast from 'const char *' to 'char*' drops const qualifier [-Werror,-Wcast-qual]_"

This will allow enable LLVM_ENABLE_WERROR when build with clang-cl on Windows.
This is imported from https://github.com/openbsd/src/commit/b81763002452802e4f7304ea60f121253bd94

Also removed the gcc change for the cast-qual warning which is not needed with const qualifier added.