arm: fix ICE with vectorized reciprocal division [PR108120]

The expand pattern for reciprocal division was enabled for all math
optimization modes, but the patterns it was generating were not
enabled unless -funsafe-math-optimizations were enabled, this leads to
an ICE when the pattern we generate cannot be recognized.

Fixed by only enabling vector division when doing unsafe math.

gcc:

	PR target/108120
	* config/arm/neon.md (div<VCVTF:mode>3): Rename from div<mode>3.
	Gate with ARM_HAVE_NEON_<MODE>_ARITH.

gcc/testsuite:
	PR target/108120
	* gcc.target/arm/neon-recip-div-1.c: New file.