Added missing #include.

Author: David Ungar

lib/Driver/ToolChain.cpp

@@ -21,6 +21,7 @@
 #include "swift/Driver/Compilation.h"
 #include "swift/Driver/Driver.h"
 #include "swift/Driver/Job.h"
+#include "swift/Option/Options.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Option/ArgList.h"