- Cmake errored out due to the ANDROID_NDK_* variables being used before being set/detected for the first time.
- Fixed one warning regarding one string replace in CMake.
- Fixed warnings when compiling SFML-Activity.
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.
