Revert "Revert "Devise a package-private means to determine the LLVM version string""

We probably just need to touch LLVM's configure this time to work around the
totally inadequate Makefile build server integration.

This reverts commit r210314.

llvm-svn: 210320
diff --git a/clang/lib/Basic/Version.cpp b/clang/lib/Basic/Version.cpp
index ae32c01..c2b7753 100644
--- a/clang/lib/Basic/Version.cpp
+++ b/clang/lib/Basic/Version.cpp
@@ -13,7 +13,7 @@
 
 #include "clang/Basic/Version.h"
 #include "clang/Basic/LLVM.h"
-#include "llvm/Config/config.h"
+#include "clang/Config/config.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdlib>
 #include <cstring>
@@ -130,7 +130,7 @@
 
   // If vendor supplied, include the base LLVM version as well.
 #ifdef CLANG_VENDOR
-  OS << " (based on LLVM " << PACKAGE_VERSION << ")";
+  OS << " (based on " << BACKEND_PACKAGE_STRING << ")";
 #endif
 
   return OS.str();