i386: Set cfun->machine->max_used_stack_alignment if needed

i386: Set cfun->machine->max_used_stack_alignment if needed

cfun->machine->max_used_stack_alignment is used to decide how stack frame
should be aligned.  This is independent of any psABIs nor 32-bit vs 64-bit.
It is always safe to compute max_used_stack_alignment.  We compute it only
if 128-bit aligned load/store may be generated on misaligned stack slot
which will lead to segfault.

gcc/

	PR target/86386
	* config/i386/i386.c (ix86_finalize_stack_frame_flags): Set
	cfun->machine->max_used_stack_alignment if needed.

gcc/testsuite/

	PR target/86386
	* gcc.target/i386/pr86386.c: New file.

From-SVN: r263317