compiler.pri: fix erronous QMAKE_FLAGS overwrite.
compiler.pri: fix erronous QMAKE_FLAGS overwrite.

SuperNascher/mumble,SuperNascher/mumble,LuAPi/mumble,austinliou/mumble,LuAPi/mumble,LuAPi/mumble,austinliou/mumble,Lartza/mumble,LuAPi/mumble,LuAPi/mumble,LuAPi/mumble,austinliou/mumble,LuAPi/mumble,SuperNascher/mumble,SuperNascher/mumble,austinliou/mumble,SuperNascher/mumble,unascribed/mumble,Lartza/mumble,SuperNascher/mumble,unascribed/mumble,LuAPi/mumble,austinliou/mumble,unascribed/mumble,unascribed/mumble,Lartza/mumble,Lartza/mumble,SuperNascher/mumble,SuperNascher/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,austinliou/mumble,unascribed/mumble,SuperNascher/mumble,unascribed/mumble,Lartza/mumble,unascribed/mumble,austinliou/mumble,austinliou/mumble,LuAPi/mumble,unascribed/mumble