3rdparty/fx11-build-shared: set _WIN32_WINNT to 0x0501.
3rdparty/fx11-build-shared: set _WIN32_WINNT to 0x0501.

In some configurations, fx11 will use symbols like CreateFile2
that are only available on Windows 8 and greater.

This change forces the library to only use APIs that are
available on Windows XP.

Fixes #1666

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