Fix relocations with multiple devices.

Fix relocations with multiple devices.

2019-09-10  Andrew Stubbs  <ams@codesourcery.com>

	libgomp/
	* plugin/plugin-gcn.c (obstack_chunk_alloc): Delete.
	(obstack_chunk_free): Delete.
	(obstack.h): Remove include.
	(create_and_finalize_hsa_program): Remove all unmodified_sections_os
	and use sections directly from the issue.
	Use "or 0x80" instead of SHT_NOTE to hide relocations, and then
	simply recognise that ourselves.

(cherry picked from openacc-gcc-9-branch commit
9e56738ddf5a5574ee67065096e19e8d73e993e0)