add new optimization level option (gcc4.6)

A new general optimization level, -Ofast, has been introduced. It combines the existing optimization level -O3 with options that can affect standards compliance but result in better optimized code. For example, -Ofast enables -ffast-math.
http://gcc.gnu.org/gcc-4.6/changes.html

Signed-off-by: Dennis Rassmann <showp1984@gmail.com>