GCN: The original meaning of 'GCN_SUPPRESS_HOST_FALLBACK' isn't applicable...

GCN: The original meaning of 'GCN_SUPPRESS_HOST_FALLBACK' isn't applicable (non-shared memory system)

'GCN_SUPPRESS_HOST_FALLBACK' originated as 'HSA_SUPPRESS_HOST_FALLBACK' in the
libgomp HSA plugin, where the idea was -- in my understanding -- that you
wouldn't have device code available for all functions that may be called, and
in that case transparently (shared memory system!) do host-fallback execution.
Or, with 'HSA_SUPPRESS_HOST_FALLBACK' set, you'd get those diagnosed.

This has then been copied into the libgomp GCN plugin as
'GCN_SUPPRESS_HOST_FALLBACK'.  However, the original meaning isn't applicable
for the libgomp GCN plugin anymore: we assume that we're generating device code
for all relevant functions, and we're implementing a non-shared memory system,
where we cannot transparently do host-fallback execution for individual
functions.

However, 'GCN_SUPPRESS_HOST_FALLBACK' has gained an additional meaning, to
enforce a fatal error in case that 'libhsa-runtime64.so.1' can't be dynamically
loaded; keep that meaning.

	libgomp/
	* plugin/plugin-gcn.c (GOMP_OFFLOAD_can_run): Don't consider
	'GCN_SUPPRESS_HOST_FALLBACK' anymore (assume always-'true').
	(init_hsa_context): Adjust 'GCN_SUPPRESS_HOST_FALLBACK' error
	message.