bswap: Fix up bswap_view_convert after the recent change [PR99882]

bswap: Fix up bswap_view_convert after the recent change [PR99882]

Martin reported that my recent change to allow pointer types in bswap
broke valgrind.  The bswap_view_convert function used for the initialization
of vector CONSTRUCTOR from the identity or byte-swapped pieces unfortunately
didn't handle pointer types.  The following patch handles it there.

2021-04-03  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/99882
	* gimple-ssa-store-merging.c (bswap_view_convert): Handle val with
	pointer type.

	* gcc.dg/pr99882.c: New test.