[Pixman] iOS support for ARM NEON

[Bobby Salazar]

With hundreds and hundreds of millions of iOS devices sold worldwide
(all having ARM processors, and the majority having ARMv7 NEON
support), it would be great to be able to use the ARM NEON fast paths
in pixman on these platforms.

Unfortunately, it seems the ARM NEON fast paths are implemented using
.S assembly files instead of compiler intrinsics. Normally this
wouldn't be a problem, except that it seems that these .S files
utilize gcc directives not supported by the Apple version of gcc
(forked long ago) or even the newer Apple LLVM compiler.

I would try to fix this myself, but I just don't understand ARM
assembly or ARM NEON instructions.

Is there anyone here who would be willing to work with me to produce a
version of the .S files compatible with both the normal/modern gcc and
the Apple versions of gcc? I'm willing to spend the time to compile
and test the code on these platforms, but I need someone to help edit
the code, ideally someone who understands it.

Any takers?