[flang] Accept OPEN(ACCESS='APPEND') legacy extension even without warnings enabled

[klausler]

Summary

My earlier patch to accept ACCESS='APPEND' only worked when warnings
were enabled; fix it.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/lib/Semantics/check-io.cpp

static std::unordered_map<IoSpecKind, const std::set<std::string>> specValues{
           // Open values; Close values are {"DELETE", "KEEP"}.
           {"NEW", "OLD", "REPLACE", "SCRATCH", "UNKNOWN"}},
       {IoSpecKind::Carriagecontrol, {"LIST", "FORTRAN", "NONE"}},
       {IoSpecKind::Convert, {"BIG_ENDIAN", "LITTLE_ENDIAN", "NATIVE"}},
       {IoSpecKind::Dispose, {"DELETE", "KEEP"}},
   };
   auto upper{parser::ToUpperCaseLetters(value)};
   if (specValues.at(specKind).count(upper) == 0) {
-    if (specKind == IoSpecKind::Access && upper == "APPEND" &&
-        context_.languageFeatures().ShouldWarn(
+    if (specKind == IoSpecKind::Access && upper == "APPEND") {
+      if (context_.languageFeatures().ShouldWarn(
               common::LanguageFeature::OpenAccessAppend)) {
-      context_.Say(source, "ACCESS='%s' interpreted as POSITION='%s'"_en_US, value, upper);
+        context_.Say(source, "ACCESS='%s' interpreted as POSITION='%s'"_en_US,
+            value, upper);
+      }
     } else {
       context_.Say(source, "Invalid %s value '%s'"_err_en_US,
           parser::ToUpperCaseLetters(common::EnumToString(specKind)), value);
     }
   }
 }
 
 // CheckForRequiredSpecifier and CheckForProhibitedSpecifier functions