i386: Require just 32-bit alignment for SLOT_FLOATxFDI_387 -m32 -mpreferred-stack...

i386: Require just 32-bit alignment for SLOT_FLOATxFDI_387 -m32 -mpreferred-stack-boundary=2 DImode temporaries [PR109276]

The following testcase ICEs since r11-2259 because assign_386_stack_local
-> assign_stack_local -> ix86_local_alignment now uses 64-bit alignment
for DImode temporaries rather than 32-bit as before.
Most of the spots in the backend which ask for DImode temporaries are during
expansion and those apparently are handled fine with -m32
-mpreferred-stack-boundary=2, we dynamically realign the stack in that case
(most of the spots actually don't need that alignment but at least one
does), then 2 spots are in STV which I assume also work correctly.
But during splitting we can create a DImode slot which doesn't need to be
64-bit alignment (it is nicer for performance though), when we apparently
aren't able to detect it for dynamic stack realignment purposes.

The following patch just makes the slot 32-bit aligned in that rare case.

2023-03-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/109276
	* config/i386/i386.cc (assign_386_stack_local): For DImode
	with SLOT_FLOATxFDI_387 and -m32 -mpreferred-stack-boundary=2 pass
	align 32 rather than 0 to assign_stack_local.

	* gcc.target/i386/pr109276.c: New test.