[compiler-rt] Fix building the aarch64 out-of-line atomics assembly for non-ELF platforms

Move the two different definitions of FUNC_ALIGN out of the ELF
specific block. Add the missing CFI_END in
END_COMPILERRT_OUTLINE_FUNCTION, to go with the corresponding CFI_START
in DEFINE_COMPILERRT_OUTLINE_FUNCTION_UNMANGLED.

Differential Revision: https://reviews.llvm.org/D92549