Unify win32-g++ and Unix qmake Makefiles.

Replace the old sed / template @FOO@ method with echo.
Enable MSYS bash to build qmake.exe
Use qmake/Makefile.unix for all win32-g++ builds.

Change-Id: I6e27d69b28d27131838bbbb3a4ee5a08b470f31b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>