This is the default when building with the clang built-in assembler,
but not if using the external assembler - thus always specify it,
for clarity.
Also use the three-operand for of a sub instruction in BS_NZC_CHECK.
The same is already done in the gnu version of the macro.
This fixes building most of the arm assembly with Apple's external
assembler. While this isn't a necessary goal in itself, there's no
harm in doing this either.
38d2d64ede