GL_COMPRESSED_RGBA_ASTC_4x4_KHR is not defined and looks to be an OpenGL ES 3.0 extension.
This fixes building on the Raspberry Pi 1-3 using VideoCore IV OpenGL ES 2.0 headers.
raspbian is built for an armv6 target, so when building for armv7, there is a problem with the ABI compatibility
for threaded applications. /usr/include/c++/*/ext/concurrence.h - undefining __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 makes it use _S_mutex
as it would when ppsspp is built for an armv6 target
see https://github.com/raspberrypi/firmware/issues/491#issuecomment-151723041
fixes problems found by users on #7479