Create GCN-specific gthreads

Create GCN-specific gthreads

2019-06-25  Kwok Cheung Yeung  <kcy@codesourcery.com>
            Andrew Stubbs  <ams@codesourcery.com>

        gcc/
	* config.gcc (thread_file): Set to gcn for AMD GCN.
	* config/gcn/gcn.c (gcn_emutls_var_init): New function.
	(TARGET_EMUTLS_VAR_INIT): New hook.

	config/
	* gthr.m4 (GCC_AC_THREAD_HEADER): Add case for gcn.

	libgcc/
	* configure: Regenerate.
	* config/gcn/gthr-gcn.h: New.

Co-Authored-By: Andrew Stubbs <ams@codesourcery.com>
From-SVN: r272647