pulseaudio: fix for ARM thumb + frame pointers compilation error
When compiling for Thumb or Thumb2, frame pointers _must_ be disabled
since the Thumb frame pointer in r7 clashes with pulseaudio's use of inline
asm to make syscalls (where r7 is used for the syscall NR).
In most cases, frame pointers will be disabled automatically due to
the optimisation level, but appending an explicit -fomit-frame-pointer
to CFLAGS handles cases where optimisation is set to -O0 or frame
pointers have been enabled by -fno-omit-frame-pointer earlier in
CFLAGS, etc.
