arm-arch.c: Remove #if 0 code.

It makes things hard to read and to grep.
Remove usage of alloc_number on "supported" platforms.

No more alloc_* on x86oids, ppc and ARM.
The last usage of alloc_number was for heap_exhausted_error, but since
the numbers are double word aligned, they can be passed as fixnums
into lisp and bignums can be safely allocated there.
Restore sb-safepoint-strictly build on non-win32.

Stray usage of alloc_sap.

Reported by Stelian Ionescu.
ARM ALLOCATION, avoid overflows.

Use an unsigned comparison against the end of allocation, otherwise it
may overflow.