tree-optimization/110556 - tail merging still pre-tuples

The stmt comparison function for GIMPLE_ASSIGNs for tail merging
still looks like it deals with pre-tuples IL.  The following
attempts to fix this, not only comparing the first operand (sic!)
of stmts but all of them plus also compare the operation code.

	PR tree-optimization/110556
	* tree-ssa-tail-merge.cc (gimple_equal_p): Check
	assign code and all operands of non-stores.

	* gcc.dg/torture/pr110556.c: New testcase.

(cherry picked from commit 7b16686e)