[Android] Dropped stlport in favor of libc++ which supports C++11
[Android] Fixed invalid drawable error
[Android] Updated scripts to use libc++ when building extlibs
[Android] Forgot to add EGLCheck.cpp to the list of file to build
[Android] Updated the Android CMake toolchain to use libc++ instead of stlport

Warning: I kept the same variable name because this file will be rewritten fairly soon since most of its code no longer applies to SFML and becomes incorrect (too hard to maintain).
Thus stlport variable names refers to libc++ stuff. E.g: ANDROID_USE_STLPORT=1 turns the use of libc++ on.