dojump: Fix gcc.dg/torture/pr91323.c for aarch64 targets

dojump: Fix gcc.dg/torture/pr91323.c for aarch64 targets

PR91323 was fixed for x86 and sparc in target code, but aarch64
instead relies on the target-independent comparison splitters.
Since LTGT is an unordered-signalling operation, we should split
it into unordered-signalling operations for any input that could
be NaN, not just inputs that could be signalling NaNs.

2020-01-27  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* dojump.c (split_comparison): Use HONOR_NANS rather than
	HONOR_SNANS when splitting LTGT.