clang:substitute -mfpu=neon-vfpv4 for -mfpu=neon

Clang 3.5 doesn't support neon-vfpv4 so fall back to neon

Change-Id: Ife58c14a42572e03b994c46ff6ee59d2b1f2637b
Signed-off-by: Maxime Poulain <maxime.poulain@student.uclouvain.be>