Merge the ./config directory between GCC and Binutils

Merge the ./config directory between GCC and Binutils

This pulls in the missing Binutils pieces into the ./config
directory. Contains these missing Binutils changes:

2014-08-14  Alan Modra  <amodra@gmail.com>

	* plugins.m4: Test for dlfcn.h or windows.h here to set default
	for --enable-plugins.  Report error if someone tries to enable
	plugins on a host we don't support.

2014-08-19  Alan Modra  <amodra@gmail.com>

	* plugins.m4 (AC_PLUGINS): If plugins are enabled, add -ldl to
	LIBS via AC_SEARCH_LIBS.

For this commit:

2014-11-26  Jan-Benedict Glaw  <jbglaw@lug-owl.de>

	* config/plugins.m4: Merge from Binutils.

From-SVN: r218102