apply neon-vfpv4 mfpu flag for cortex-a15 cpu

Change-Id: I663d8b0c169113727dd2c5c12c0c896d2d8efe20
arm:thumb:compiling with  O2

The compiler was targeting -Os before this commit, now it targets -O2

Change-Id: I07929b161610acd0a2cebb63a383720b6078d59c
clang:compiling with O3 flag

Change-Id: Id4d56ee3b6b250674df852ff8b1c583c3c80f0fc
Enabled gcc's automatic vectorization for the whole build

Change-Id: Idfcc7f1810605308d64667c06e2b1b823a6cee7c
No error on array-bounds

O3 flag raises an error when array subscript is above array bounds, passing Wno-array-bounds prevents the compiler to stop working when facing this error

Change-Id: Ide8d80360bb2ee351b8aa5bebb4a2c1f58a26ea7