Many places check for the string 'GCC' in sys.version to identify a 'posix' build. Remove anchor from regex for extracting version number from -v/--version output. The presence of a git commit hash in LLD's ld -v output was confusing it. This doesn't seem entirely save, but solves the immediate problem. set CC to clang on clang prefix, to fix LTO/PGO Remove mktime workaround now that mingw-w64 exports that symbol.