Add support for tilegx in gold.

Add support for tilegx in gold.
	* configure.ac (ENABLE_GOLD): support tilegx*
	* configure: rebuild
elfcpp:
	* tilegx.h: New file.
	* elfcpp.h: add EM_TILEGX.
gold:
	* tilegx.cc: New file.
	* Makefile.am (TARGETSOURCES): Add tilegx.cc
	(ALL_TARGETOBJS): Add tilegx.$(OBJEXT)
	* configure.tgt: Add entries for tilegx*.
	* configure.ac: Likewise.
	* Makefile.in: Rebuild.
	* configure: Likewise.
	* testsuite/icf_safe_test.sh (arch_specific_safe_fold): Handle
	tilegx.