buildgcc: Add patch for building binutils by clang 6.0

Clang is the default compiler on BSD and OS X. With this
change, we don't have to install gcc any more. Clang can
act as host cc.
This is a known issue on GNU mail list. Please refer
the link below.
https://sourceware.org/bugzilla/show_bug.cgi?id=17473

Change-Id: I0f014b776e86e6d0cbebd560cb17f469f31e1dfb
Signed-off-by: Zheng Bao <zheng.bao@amd.com>
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: http://review.coreboot.org/11638
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/crossgcc/patches/binutils-2.25_host-clang.patch

@@ -0,0 +1,18 @@
+This is a known issue on GNU mail list. Please refer
+the link below.
+https://sourceware.org/bugzilla/show_bug.cgi?id=17473
+
+--- binutils-2.25/gold/binary.cc	2014-10-14 00:32:04.000000000 -0700
++++ binutils-2.25.patched/gold/binary.cc	2015-09-15 07:02:40.000000000 -0700
+@@ -24,10 +24,10 @@
+ 
+ #include <cerrno>
+ #include <cstring>
++#include "stringpool.h"
+ #include "safe-ctype.h"
+ 
+ #include "elfcpp.h"
+-#include "stringpool.h"
+ #include "fileread.h"
+ #include "output.h"
+ #include "binary.h"