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.
Hoist up some typechecks to avoid emitting them repeatedly.

Also simplify some bitwise ops.
Add FIXME about some probably obsolete code.
Fix truncate type derivation.

Make sure SB-C::INTERVAL-DIV returns an interval, and not just NIL.

Fixes lp#1389428.
Slight improvement to SLOT-{VALUE,BOUNDP,MAKUNBOUND} etc.
Make early class predicates (CLASSP etc) get source locations.
Remove double negative