When compiling an OpenMP or OpenACC program containing a reference in the
offloaded code to a symbol that has not been included in the offloaded code,
the offloading compiler may ICE in lto1.

Fix this by erroring out instead, mentioning the problematic symbol:
...
error: variable 'var' has been referenced in offloaded code but hasn't
  been marked to be included in the offloaded code
lto1: fatal error: errors during merging of translation units
compilation terminated.
...

Build x86_64 with nvptx accelerator and reg-tested libgomp.

Build x86_64 and reg-tested libgomp.

2018-12-14  Tom de Vries  <tdevries@suse.de>

	* lto-cgraph.c (verify_node_partition): New function.
	(input_overwrite_node, input_varpool_node): Use verify_node_partition.

	* testsuite/libgomp.c-c++-common/function-not-offloaded-aux.c: New test.
	* testsuite/libgomp.c-c++-common/function-not-offloaded.c: New test.
	* testsuite/libgomp.c-c++-common/variable-not-offloaded.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/function-not-offloaded.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/variable-not-offloaded.c: New test.

From-SVN: r267134