[flang][OpenMP] Fix symbol handling in critical constructs

Fixes llvm#78936

Author: luporl

flang/lib/Semantics/resolve-directives.cpp

@@ -1823,6 +1823,7 @@ bool OmpAttributeVisitor::Pre(const parser::OpenMPCriticalConstruct &x) {
   const auto &beginCriticalDir{std::get<parser::OmpCriticalDirective>(x.t)};
   const auto &endCriticalDir{std::get<parser::OmpEndCriticalDirective>(x.t)};
   PushContext(beginCriticalDir.source, llvm::omp::Directive::OMPD_critical);
+  GetContext().withinConstruct = true;
   if (const auto &criticalName{
           std::get<std::optional<parser::Name>>(beginCriticalDir.t)}) {
     ResolveOmpName(*criticalName, Symbol::Flag::OmpCriticalLock);