prevent qmake from appending -Xarch_x86_64
prevent qmake from appending -Xarch_x86_64

because gcc and g++ do not have this option, only clang and clang++.
johnyf/slugs,LTLMoP/slugs,LTLMoP/slugs,LTLMoP/slugs,johnyf/slugs,LTLMoP/slugs,johnyf/slugs,LTLMoP/slugs