fix autoconf build from r133710
Sorry! This commit worked in CMake, but
CXX_INCLUDE_ROOT is defined in a different
config.h for autoconf.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133715 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 4cd96be..5eb8594 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -36,6 +36,8 @@
#include <cstdlib> // ::getenv
+#include "llvm/Config/config.h" // for CXX_INCLUDE_ROOT
+
using namespace clang::driver;
using namespace clang::driver::toolchains;