Select the correct target STL with USE_MINGW.
Select the correct target STL with USE_MINGW.

The previous check tested against USE_MINGW even for target builds.
Hadn't been a problem because people don't typically set USE_MINGW
directly.

Change-Id: I90fe0ea890c44917eb29dd02d7c7f76c19e7fbd6

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build