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.
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