add cflags for -mtune to target arch variant

Change-Id: I0b3693ce2f478e52d559d6007d1ae50830aa4d72
enable bionic NEON optimization to TARGET_ARCH_VARIANT_CPU

Change-Id: Ie5c87dd24c8475b9aaa2117b8aed9abc6ea9657a
more precision in ARMv7-a flags

Change-Id: I72d6cd0a8c495bb500187a91ba01cb3d2ea561ed
use ffast-math:

since ffast math implies funsafe-math-optimizations and a few others.. use this instead

Change-Id: I6d00351318675ece1418305ccfb8a494fc8440e8