bswap: Handle bswapping of pointers [PR96573]

bswap: Handle bswapping of pointers [PR96573]

In GCC8/9 we used to optimize this into a bswap, but we no longer do.
Handling byteswapping of pointers is easy, all we need is to allow them,
for the __builtin_bswap* we already use TYPE_PRECISION to determine
the precision and we cast the operand and result to the correct type
if they aren't uselessly convertible to what the builtin expects.

2021-04-01  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96573
	* gimple-ssa-store-merging.c (init_symbolic_number): Handle
	also pointer types.

	* gcc.dg/pr96573.c: New test.