More cmake patches (android, emscripten)

most of these patches are there to fix the android build with cmake

https://bugzilla.libsdl.org/show_bug.cgi?id=3201
https://bugzilla.libsdl.org/show_bug.cgi?id=3200
https://bugzilla.libsdl.org/show_bug.cgi?id=3197

with these patches applied, you don’t have to use the preconfigured android
config header anymore.

afair I already posted about this patch:
https://bugzilla.libsdl.org/show_bug.cgi?id=3194 (added some more details
there as comment, too)

Regards
Martin–
http://www.caveproductions.org