It was using ':' as a path separator while GCC uses ';' resulting in bogus
paths being returned. Instead assume that the compiler uses the platform native
separator.
The previous splitting code still worked sometimes because splitting
"C:/foo;C:/bar" resulted in the last part "/bar" being valid if "<DriveOfCWD>:/bar"
existed.
The fix also exposes a clang Windows bug where it uses the wrong separator:
https://reviews.llvm.org/D61121 . Use a regex to fix those first.
This resulted in linker errors when statically linking against a library which
had an external dependency linking against system libs.
Fixes#5386
7ce9e56a4b