What changed in EDuke32, build by build

Modify ProcessRGB to take input in RGBA format instead of BGRA.

Enforce C linkage on the ProcessRGB functions.

Replace use of std::array (which seems not to exist under all compilers) with simple custom class.

Replace x86-specific _bswap intrinsic with custom byteswap function (which a good compiler should treat identically anyway).

Remove C++11 dependency on cstdint when compiling with an earlier standard revision.

Modify include guard tokens to conform to the C and C++ standards by not using underscore prefixes.

Remove SSE4.1 and AVX2 support.

The fma function is not a member of the std namespace.

Fix type problem in ProcessRGB_ETC2.