Add a missing include to translation_unit - required after the roll to clang r277962.

tools/clang/translation_unit/TranslationUnitGenerator.cpp

Index: tools/clang/translation_unit/TranslationUnitGenerator.cpp
diff --git a/tools/clang/translation_unit/TranslationUnitGenerator.cpp b/tools/clang/translation_unit/TranslationUnitGenerator.cpp
index 3590b0c4ea30d7a1719e1a16348e42b2397070e9..4d7524d90ab544b68ac4daa7028d321dbb13998c 100644
--- a/tools/clang/translation_unit/TranslationUnitGenerator.cpp
+++ b/tools/clang/translation_unit/TranslationUnitGenerator.cpp
@@ -31,6 +31,7 @@
 #include "clang/Tooling/Refactoring.h"
 #include "clang/Tooling/Tooling.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Path.h"
 
 using clang::HeaderSearchOptions;
 using clang::tooling::CommonOptionsParser;