Added GCC optimizations, SDL system and 7z/LZMA fixes

+Added unsigned int i fixes to Heretic/Hexen codepointers for GCC
optimization (edward-san/BZlut3)
+Fixed edward-san's typo in SDL/i_system.cpp (BZlut3)
+Added minor fixes for new LZMA SDK on non-Win32/Win64 targets