[flang] Add missing include, fix build break after c81a189 (llvm#169192)

Author: kparzysz

flang/lib/Semantics/canonicalize-do.cpp

@@ -9,6 +9,7 @@
 #include "canonicalize-do.h"
 #include "flang/Parser/openmp-utils.h"
 #include "flang/Parser/parse-tree-visitor.h"
+#include "flang/Parser/tools.h"
 
 namespace Fortran::parser {