tree-optimization/112909 - uninit diagnostic with abnormal copy

tree-optimization/112909 - uninit diagnostic with abnormal copy

The following avoids spurious uninit diagnostics for SSA name
copies which mostly appear when the source is marked as abnormal
which prevents copy propagation.

To prevent regressions I remove the bail out for anonymous SSA
names in the PHI arg place from warn_uninitialized_phi leaving
that to warn_uninit where I handle SSA copies from a SSA name
which isn't anonymous.  In theory this might cause more
valid and false positive diagnostics to pop up.

	PR tree-optimization/112909
	* tree-ssa-uninit.cc (find_uninit_use): Look through a
	single level of SSA name copies with single use.

	* gcc.dg/uninit-pr112909.c: New testcase.