gimple-fold: fix further missing stmt locations [PR104308]

gimple-fold: fix further missing stmt locations [PR104308]

PR analyzer/104308 initially reported about a
-Wanalyzer-use-of-uninitialized-value diagnostic using UNKNOWN_LOCATION
when complaining about certain memmove operations where the source
is uninitialized.

In r12-7856-g875342766d4298 I fixed the missing location for
a stmt generated by gimple_fold_builtin_memory_op, but the reporter
then found another way to generate such a stmt with UNKNOWN_LOCATION.

I've now gone through gimple_fold_builtin_memory_op looking at all
statement creation, and found three places in which a new statement
doesn't have a location set on it (either directly via
gimple_set_location, or indirectly via gsi_replace), one of which is
the new reproducer.

This patch adds a gimple_set_location to these three cases, and adds
test coverage for one of them (the third hunk within the patch), fixing
the new reproducer for PR analyzer/104308.

gcc/ChangeLog:
	PR analyzer/104308
	* gimple-fold.cc (gimple_fold_builtin_memory_op): Explicitly set
	the location of new_stmt in all places that don't already set it,
	whether explicitly, or via a call to gsi_replace.

gcc/testsuite/ChangeLog:
	PR analyzer/104308
	* gcc.dg/analyzer/pr104308.c: Add test coverage.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>