Fix gold incremental test failures.

Fix gold incremental test failures.

Newer version of GCC pass -z relro to the linker, but incremental linking
does not support relro. This patch adds a check to complain about the
conflict, and changes the testsuite to pass -z norelro to the incremental
tests.

2015-03-11  Cary Coutant  <ccoutant@google.com>

gold/
	* options.cc (General_options::finalize): Don't allow -z relro
	with incremental linking.
	* testsuite/Makefile.am (incremental_test): Add -z norelro.
	(incremental_test_2): Likewise.
	(incremental_test_3): Likewise.
	(incremental_test_4): Likewise.
	(incremental_test_5): Likewise.
	(incremental_test_6): Likewise.
	(incremental_copy_test): Likewise.
	(incremental_common_test_1): Likewise.
	(incremental_comdat_test_1): Likewise.
	* testsuite/Makefile.in: Regenerate.