Include llvm/Config/config.h.

This pulls -DHAVE_XXX_H and other useful def's into MCLinker to
remedy the lack of autotools.

Change-Id: I909fb9846e2d6a21d31d3eada48161a1faca4caa
diff --git a/include/mcld/Config/Config.h b/include/mcld/Config/Config.h
index ea92259..8daa109 100644
--- a/include/mcld/Config/Config.h
+++ b/include/mcld/Config/Config.h
@@ -14,7 +14,7 @@
 #ifndef MCLD_CONFIG_H
 #define MCLD_CONFIG_H
 
-#include <llvm/Config/llvm-config.h>
+#include <llvm/Config/config.h>
 
 #ifdef LLVM_ON_UNIX
 # define MCLD_ON_UNIX 1