compiler-rt: whitespace and uniformity for arm

Make the whitespace a bit more uniform in the various assembly routines.  This
also makes the assembly files a bit more uniform on the ARM side by explicitly
stating that it is using the unified syntax and that the contents of the code is
in the text section (or segment).  No functional change.
compiler-rt: prefer .rodata for non MachO targets

Place constants into .rdata if targeting ELF or COFF/PE.  This should be
functionally identical, however, the data would be placed into a different
section.  This is purely a cleanup change.