[binutils-gdb] Fix hidden visibility compiler test

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 629dabe3b731c6194499652301935f34c3c20e0c ***

Author: Alan Modra <amodra@gmail.com>
Branch: master
Commit: 629dabe3b731c6194499652301935f34c3c20e0c

Fix hidden visibility compiler test

Warnings from configure tests aren't usually checked.  gcc's
"visibility attribute not supported in this configuration" warning is
enabled by default so we don't need to add any warning flag except
-Werror.

	* configure.ac (bfd_cv_hidden): Run test with -Werror in CFLAGS.
	* configure: Regenerate.