Compile only the necessary file with -maes

This will likely become conditional after checking if the compiler
supports -maes or equivalent.
Allow code to be run during the build process
aes_aesni.c is a better name
Wrap __get_cpuid with a CPUSUPPORT ifdef
Wrap stdio.h with DEBUG ifdef

The stdio.h header is only used for checking if AESNI is enabled.
Use -O2 and force CPUSUPPORT_X86_CPUID to be set