Modify gold testsuite to disable plugins added by GCC driver.

Modify gold testsuite to disable plugins added by GCC driver.

GCC 4.8 now adds linker plugin options by default, which conflict with the
--incremental tests in the testsuite. This patch checks whether the compiler
supports the -fno-use-linker-plugin option, and adds it to all link
commands.

2014-04-02  Cary Coutant  <ccoutant@google.com>

	* configure.ac (HAVE_PUBNAMES): Use C instead of C++.
	(HAVE_NO_USE_LINKER_PLUGIN): Check for -fno-use-linker-plugin.
	* configure: Regenerate.
	* testsuite/Makefile.am (OPT_NO_PLUGINS): New macro for
	-fno-use-linker-plugin.
	(LINK1, CXXLINK1): Add it to the link command.
	* testsuite/Makefile.in: Regenerate.