binutils: disable plugins for static links

Plugins want to use dlopen even when configured with --disable-shared.
Add --disable-plugins when STATIC_LIBS is selected.
Fixes:
  http://autobuild.buildroot.net/results/a59e5858d777dcee3d8f7fb6e82ee4735b520155/

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/binutils/binutils.mk

@@ -51,6 +51,10 @@ BINUTILS_CONF_OPTS = \
 	$(BINUTILS_DISABLE_GDB_CONF_OPTS) \
 	$(BINUTILS_EXTRA_CONFIG_OPTIONS)
 
+ifeq ($(BR2_STATIC_LIBS),y)
+BINUTILS_CONF_OPTS += --disable-plugins
+endif
+
 # Don't build documentation. It takes up extra space / build time,
 # and sometimes needs specific makeinfo versions to work
 BINUTILS_CONF_ENV += ac_cv_prog_MAKEINFO=missing