Add the ability to pass the path to binutils source to configure. This is
needed to build the LLVM gold plugin.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63621 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Makefile.config.in b/Makefile.config.in
index bcf1a00..90d1a13 100644
--- a/Makefile.config.in
+++ b/Makefile.config.in
@@ -283,3 +283,6 @@
 else
   SYSPATH = $(1)
 endif
+
+# Location of the plugin header file for gold.
+BINUTILS_INCDIR := @BINUTILS_INCDIR@