[flang] Prevent bogus runtime I/O error message

The runtime was requiring that STATUS='OLD' be explicitly specified
on an OPEN statement for a connected unit.  There error should issue
only if a STATUS= other than 'OLD' is specified; an OPEN with no
STATUS= specifier is okay.

Reviewed By: sscalpone

Differential Revision: https://reviews.llvm.org/D84079

Author: klausler

flang/runtime/io-stmt.cpp

@@ -162,11 +162,12 @@ void OpenStatementState::set_path(
 }
 
 int OpenStatementState::EndIoStatement() {
-  if (wasExtant_ && status_ != OpenStatus::Old) {
-    SignalError("OPEN statement for connected unit must have STATUS='OLD'");
+  if (wasExtant_ && status_ && *status_ != OpenStatus::Old) {
+    SignalError("OPEN statement for connected unit may not have STATUS= other "
+                "than 'OLD'");
   }
-  unit().OpenUnit(
-      status_, action_, position_, std::move(path_), pathLength_, *this);
+  unit().OpenUnit(status_.value_or(OpenStatus::Unknown), action_, position_,
+      std::move(path_), pathLength_, *this);
   return ExternalIoStatementBase::EndIoStatement();
 }
 

flang/runtime/io-stmt.h

@@ -302,7 +302,7 @@ class OpenStatementState : public ExternalIoStatementBase {
 
 private:
   bool wasExtant_;
-  OpenStatus status_{OpenStatus::Unknown};
+  std::optional<OpenStatus> status_;
   Position position_{Position::AsIs};
   std::optional<Action> action_;
   OwningPtr<char> path_;