Include PathV1.h only where it is used.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/Compilation.cpp b/lib/Driver/Compilation.cpp
index 50725fc..ef40ae4 100644
--- a/lib/Driver/Compilation.cpp
+++ b/lib/Driver/Compilation.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Option/ArgList.h"
+#include "llvm/Support/PathV1.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/raw_ostream.h"
 #include <errno.h>