tree-reassoc.cc: PR tree-optimization/116139 Don't assert when forming fully-pipeline...

tree-reassoc.cc: PR tree-optimization/116139 Don't assert when forming fully-pipelined FMAs on wide MULT targets

The code in get_reassociation_width that forms FMAs aggressively when
they are fully pipelined expects the FMUL reassociation width in the
target to be less than for FMAs. This doesn't hold for all target
tunings.

This code shouldn't ICE, just avoid forming these FMAs here.
This patch does that.

Signed-off-by: Kyrylo Tkachov <ktkachov@nvidia.com>
	PR tree-optimization/116139

gcc/ChangeLog:

	* tree-ssa-reassoc.cc (get_reassociation_width): Move width_mult
	<= width comparison to if condition rather than assert.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/pr116139.c: New test.