sbc: better compatibility with ARM thumb/thumb2

ARM assembly optimizations fail to compile in thumb mode, but are fine
for thumb2. Update ifdefs in the code to make use of ARM assembly only
when it is safe and also make sure that no optimizations are missed
when compiling for thumb2.

The problem was reported by Paul Menzel:
https://tango.0pointer.de/pipermail/pulseaudio-discuss/2011-February/009022.html
2 files changed