The following adjusts the sbitmap bitmap_set_bit and bitmap_clear_bit
APIs to match that of bitmap by returning a bool indicating whether
the bitmap was changed.  I've also changed bitmap_bit_p to return
a bool rather than an int and made use of the sbitmap bitmap_set_bit
API change in one place.

2021-11-03  Richard Biener  <rguenther@suse.de>

	* bitmap.h (bitmap_bit_p): Change the return type to bool.
	* bitmap.c (bitmap_bit_p): Likewise.
	* sbitmap.h (bitmap_bit_p): Likewise.
	(bitmap_set_bit): Return whether the bit changed.
	(bitmap_clear_bit): Likewise.
	* tree-ssa.c (verify_vssa): Make use of the changed state
	from bitmap_set_bit.