Check for unsupported flags (old GCC)

Apple default GCC, even in Mavericks, fails to compile before this mod
because of unsupported -W flags.
Stop uselessly defining MAY_ALIAS

The definition of MAY_ALIAS in the Makefile was supposed to improve
compiler portability, but it just replaced it with a GNU Make dependency
which is a more realistic concern.
Whitespace and vim modeline
Mend SDL2 buffering bugs