libgomp HSA/GCN plugins: don't prepend the 'HSA_RUNTIME_LIB' path to 'libhsa-runtime6...

libgomp HSA/GCN plugins: don't prepend the 'HSA_RUNTIME_LIB' path to 'libhsa-runtime64.so'

For unknown reasons, this had gotten added for the libgomp HSA plugin in commit
b8d89b03db5f212919e4571671ebb4f5f8b1e19d (r242749) "Remove build dependence on
HSA run-time", and later propagated into the GCN plugin.

	libgomp/
	* plugin/plugin-hsa.c (init_enviroment_variables): Don't prepend
	the 'HSA_RUNTIME_LIB' path to 'libhsa-runtime64.so'.
	* plugin/plugin-gcn.c (init_environment_variables): Likewise.
	* plugin/configfrag.ac (HSA_RUNTIME_LIB): Clean up.
	* config.h.in: Regenerate.
	* configure: Likewise.

(cherry picked from commit 7c1e856bedb4ae190c420ec2d2ca5e08730cf21d)