gimple-fold: Move optimizing memcpy to memset to fold_stmt from fab

gimple-fold: Move optimizing memcpy to memset to fold_stmt from fab

I noticed this folding inside fab could be done else where and could
even improve inlining decisions and a few other things so let's
move it to fold_stmt.
It also fixes PR 116601 because places which call fold_stmt already
have to deal with the stmt becoming a non-throw statement.

For the fix for PR 116601 on the branches should be the original patch
rather than a backport of this one.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/116601

gcc/ChangeLog:

	* gimple-fold.cc (optimize_memcpy_to_memset): Move
	from tree-ssa-ccp.cc and rename. Also return true
	if the optimization happened.
	(gimple_fold_builtin_memory_op): Call
	optimize_memcpy_to_memset.
	(fold_stmt_1): Call optimize_memcpy_to_memset for
	load/store copies.
	* tree-ssa-ccp.cc (optimize_memcpy): Delete.
	(pass_fold_builtins::execute): Remove code that
	calls optimize_memcpy.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr78408-1.c: Adjust dump scan to match where
	the optimization now happens.
	* g++.dg/torture/except-2.C: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>