Allow clang derived from older GCC versions to use ARM intrinsics
This causes all clang builds which use -mfpu=neon to use the intrinsics code,
not the assembler code.  This has only been tested on iOS 7, it may be necessary
to exclude some earlier clang versions but this seems unlikely.

Signed-off-by: John Bowler <jbowler@acm.org>
[libpng16] Allow clang derived from older GCC versions to use ARM intrinsics.
Merge branch 'libpng16' of /home/jbowler/src/libpng/libpng into libpng16

Conflicts:
	pngpriv.h