This makes the -separate-debug-info configure optional functional, which
generates dSYM debug info bundles for Qt libraries on Apple platforms.

Task-number: QTBUG-37952
Done-with: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Change-Id: Ia247674740bf450130a15db926df07fa9007e2ca
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>