osx-clang: work around Homebrew's clang lacking REG_ENHANCED#6138

dscho wants to merge 1 commit intomaingit-for-windows/git:mainfrom

fix-ci-osx-clang-and-reftables-jobsgit-for-windows/git:fix-ci-osx-clang-and-reftables-jobsCopy head branch name to clipboard