Prune removed funcs from offload table

Prune removed funcs from offload table

2017-12-30  Tom de Vries  <tom@codesourcery.com>

	PR libgomp/83046
	* omp-expand.c (expand_omp_target): If in_lto_p, mark offload_funcs with
	DECL_PRESERVE_P.
	* lto-streamer-out.c (prune_offload_funcs): New function.  Remove
	offload_funcs entries that no longer have a corresponding cgraph_node.
	Mark the remaining ones as DECL_PRESERVE_P.
	(output_lto): Call prune_offload_funcs.

	* testsuite/libgomp.oacc-c-c++-common/pr83046.c: New test.
	* testsuite/libgomp.c-c++-common/pr83046.c: New test.

From-SVN: r256045