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.
Previously the assembly sources had mixed indentation consisting
of both spaces and tabs, making it quite hard to read unless
the right tab size was used in the editor.
Tabs have been interpreted as 4 spaces in most cases, matching
the surrounding code.
