- Shut up GCC aggressive optimizer warnings.

From what I can see, GCC would miscompile the involved loops, because the index variable is 'signed int' and the multiplication with an unsigned would cause signed overflow (undefined behavior). Change the index variable type to 'unsigned int' to expect unsigned overflow (conformant to standard).
- Simplify CMake GCC and Clang checking.

Introduce the variable 'ZD_CMAKE_COMPILER_IS_GNUC(XX)_COMPATIBLE' and replace any occurrence of '"${CMAKE_C(XX)_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_C(XX)_COMPILER_ID}" STREQUAL "Clang"' with it. This makes it possible to add more GCC compatible compilers in just one place.
- Using USE_WINDOWS_DWORD on other platforms can cause problems.
Merge branch 'edward-san-cmake_gcc_compatible'
Merge branch 'gcc_aggressive_optimization' of github.com:edward-san/zdoom into edward-san-gcc_agressive_optimization
Merge branch 'master' of https://github.com/rheit/zdoom

Conflicts:
	src/CMakeLists.txt
- Fixed edward-san's typo.
- Cleared a warning.
Use byte swapping functions from <libkern/OSByteOrder.h> on OS X

Remove inclusion of Core Foundation headers to avoid type conflicts with LZMA SDK.
Use correct 'true' keyword
Fix incorrect actor flag handling on big endian platforms
Merge pull request #78 from alexey-lysiuk/fix_osx_build

Fix OS X build
- fixed: transferring a translation to a missile needs to check if the missile was spawned successfully.
Merge branch 'master' of https://github.com/rheit/zdoom
- fixed: When the 3D floor init code was updated 5 years ago for Vavoom's latest changes to its 3D-floor implementation it accidentally set the 3D-floor's alpha as its desaturation.
Merge branch 'master' of https://github.com/rheit/zdoom