Fixed LuaJIT build on Linux, both native and cross-compiling.

The following platforms should be now supported:
Windows, Linux, Mac OS X, IOS, Android, and Raspberry Pi. Not all platforms are fully tested yet.

Cross-compilation may work on GCC/CLang only.
Fixed LuaJIT CMake error on Windows platform.
Workaround for VS2008 64-bit mode.
Fixed 32-bit LuaJIT compilation on Linux platform.
Rephrased instructions to overcome CMake error for LuaJIT cross-compilation build.