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

This didn't work out on the build servers. Investigating

This reverts commit r210313.

llvm-svn: 210314
diff --git a/clang/lib/Basic/Version.cpp b/clang/lib/Basic/Version.cpp
index c2b7753..ae32c01 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 "clang/Config/config.h"
+#include "llvm/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 " << BACKEND_PACKAGE_STRING << ")";
+  OS << " (based on LLVM " << PACKAGE_VERSION << ")";
 #endif
 
   return OS.str();