For SLE-12 explicitely add std=gnu++11 to CXX for gold.

It's configured and set "correctly" in the gold subdir, but the toplevel
passes CXX=g++ down (and that overrides), so hack around this.

OBS-URL: https://build.opensuse.org/package/show/devel:gcc/binutils?expand=0&rev=460

binutils.spec

@@ -359,6 +359,7 @@ cd build-dir
 	--enable-threads \
 %endif
 %if %{suse_version} <= 1320
+	CXX="g++ -std=gnu++11" \
 	--disable-x86-relax-relocations \
 	--disable-compressed-debug-sections \
 %endif