[testsuite] Add scan-offload-tree-dump

[testsuite] Add scan-offload-tree-dump

2018-05-03  Tom de Vries  <tom@codesourcery.com>

	PR testsuite/85106
	* lib/scanoffloadtree.exp: New file.

	* testsuite/lib/libgomp-dg.exp (libgomp-dg-test): Add save-temps to
	extra_tool_flags if it contains an -foffload=-fdump-* flag.
	* testsuite/lib/libgomp.exp: Include scanoffloadtree.exp.
	* testsuite/libgomp.oacc-c/vec.c: Use scan-offload-tree-dump.

	* doc/sourcebuild.texi (Commands for use in dg-final, Scan optimization
	dump files): Add offload-tree.

From-SVN: r259892