[flang] Detect image control statements in non-construct IF statements

[klausler]

Summary

The utility routine in semantics that determines whether an
executable construct constitutes an image control statement
was not examining the single action statement controlled by
a non-construct IF statement, e.g. 'IF(P) STOP'.

flang/lib/Semantics/tools.cpp

   template <typename T> bool operator()(const common::Indirection<T> &x) {
     return (*this)(x.value());
   }
+  template <typename A> bool operator()(const parser::Statement<A> &x) {
+    return (*this)(x.statement);
+  }
   bool operator()(const parser::AllocateStmt &stmt) {
     const auto &allocationList{std::get<std::list<parser::Allocation>>(stmt.t)};
     for (const auto &allocation : allocationList) {

     return std::get<parser::StopStmt::Kind>(stmt.t) ==
         parser::StopStmt::Kind::Stop;
   }
-  bool operator()(const parser::Statement<parser::ActionStmt> &stmt) {
-    return common::visit(*this, stmt.statement.u);
+  bool operator()(const parser::IfStmt &stmt) {
+    return (*this)(
+        std::get<parser::UnlabeledStatement<parser::ActionStmt>>(stmt.t)
+            .statement);
+  }
+  bool operator()(const parser::ActionStmt &stmt) {
+    return common::visit(*this, stmt.u);
   }
 
 private:

flang/test/Semantics/doconcurrent01.f90

      SYNC IMAGES (*)
 !ERROR: An image control statement is not allowed in DO CONCURRENT
      SYNC MEMORY
+!ERROR: An image control statement is not allowed in DO CONCURRENT
+     stop
+!ERROR: An image control statement is not allowed in DO CONCURRENT
+     if (.false.) stop
+     error stop ! ok
 !ERROR: RETURN is not allowed in DO CONCURRENT
      return
 10 continue