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.
This fixes building with gnu binutils, which don't support this
nonstandard form of the instructions.
Once Apple's tools support the proper standard form of the
instructions, the code should be updated to use that everywhere
instead, and these macros should be removed.
