c: Fix compile time hog in c_genericize [PR107127]

The complex multiplications result in deeply nested set of many SAVE_EXPRs,
which takes even on fast machines over 5 minutes to walk.
This patch fixes that by using walk_tree_without_duplicates where it is

2022-11-23  Andrew Pinski  <apinski@marvell.com>
	    Jakub Jelinek  <jakub@redhat.com>

	PR c/107127
	* c-gimplify.cc (c_genericize): Use walk_tree_without_duplicates
	instead of walk_tree for c_genericize_control_r.

	* gcc.dg/pr107127.c: New test.
2 files changed