On MSYS2, if QtCreator is launched from one of the msys2 shells
then the MSYSTEM env. var is set and our Pythons set os.sep and
os.path.sep to '/' so that it aligns with the default separator
of those shells.

fromNativePath(str) then fails to convert '\' seprators embedded
in binaries since str.replace('/', '/') is a noop. The operation
we want here is to convert all '\' to '/' anyway so this is more
explicit regardless of any opinions on our choice to dynamically
vary os.sep and os.path.sep

Change-Id: I76c05b188abca41c6a1b516c68b584e0c06e7235
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: hjk <hjk@theqtcompany.com>