3rdparty/fx11-build: remove DX_SDK include dir, we get it from the environment.
3rdparty/fx11-build: remove DX_SDK include dir, we get it from the environment.

Fixes the build when using Qt 5.  Qt 5's qmake includes
an unquoted "C:\Program Files (x86)\[...]" in the Makefile,
causing the build to break.

mbax/mumble,bheart/mumble,mbax/mumble,niko20010/mumble,LuAPi/mumble,ccpgames/mumble,niko20010/mumble,austinliou/mumble,ccpgames/mumble,unascribed/mumble,Zopieux/mumble,richard227/mumble,richard227/mumble,feld/mumble,Githlar/mumble,austinliou/mumble,Zopieux/mumble,Lartza/mumble,SuperNascher/mumble,feld/mumble,feld/mumble,Lartza/mumble,ccpgames/mumble,Githlar/mumble,SuperNascher/mumble,Zopieux/mumble,Keridos/mumble,SuperNascher/mumble,austinliou/mumble,Zopieux/mumble,mbax/mumble,Keridos/mumble,mbax/mumble,Keridos/mumble,Lartza/mumble,niko20010/mumble,ccpgames/mumble,Githlar/mumble,richard227/mumble,austinliou/mumble,Natenom/mumble,bheart/mumble,feld/mumble,SuperNascher/mumble,Githlar/mumble,bheart/mumble,LuAPi/mumble,Lartza/mumble,Keridos/mumble,bheart/mumble,Lartza/mumble,austinliou/mumble,richard227/mumble,Natenom/mumble,niko20010/mumble,LuAPi/mumble,Natenom/mumble,Keridos/mumble,unascribed/mumble,LuAPi/mumble,SuperNascher/mumble,feld/mumble,ccpgames/mumble,unascribed/mumble,unascribed/mumble,Keridos/mumble,austinliou/mumble,mbax/mumble,richard227/mumble,Natenom/mumble,feld/mumble,unascribed/mumble,SuperNascher/mumble,niko20010/mumble,Zopieux/mumble,Lartza/mumble,Zopieux/mumble,LuAPi/mumble,mbax/mumble,Natenom/mumble,Keridos/mumble,feld/mumble,bheart/mumble,richard227/mumble,Zopieux/mumble,Natenom/mumble,ccpgames/mumble,Lartza/mumble,feld/mumble,Lartza/mumble,mbax/mumble,austinliou/mumble,Githlar/mumble,SuperNascher/mumble,Keridos/mumble,niko20010/mumble,Githlar/mumble,SuperNascher/mumble,unascribed/mumble,niko20010/mumble,LuAPi/mumble,austinliou/mumble,Natenom/mumble,LuAPi/mumble,bheart/mumble,Natenom/mumble,Githlar/mumble,mbax/mumble,bheart/mumble,niko20010/mumble,unascribed/mumble,richard227/mumble,ccpgames/mumble,richard227/mumble,bheart/mumble,Githlar/mumble,Zopieux/mumble,unascribed/mumble,ccpgames/mumble,SuperNascher/mumble,LuAPi/mumble,LuAPi/mumble