The apple assembler for arm64 can handle the gnu binutils style
macros just fine, so there is no need to duplicate all of these
macros in two syntaxes, when the new one works fine in all cases.
We already require a new enough assembler to support the gnu binutils
style features since we use the .rept directive in a few places.
Previously this used unofficial, apple specific syntax (with fallback
macros for gnu binutils), since Xcode 5.x didn't support the official
syntax of these instructions. Since Xcode 6 has been out for quite a
number of months already, it should be safe to require this (for
building 64 bit binaries for iOS, armv7 builds can still be built
with older Xcode versions).
This clarifies the code by avoiding apple specific syntax in the
assembler instructions.
Since Xcode 5.1, the apple tools actually support using the
official, correct syntax for the ext instructions. This syntax
is already used in a number of places already - use it consistently,
and get rid of the compatibility hacks.
