[Concurrency] Fix embedded, cannot refer to runtime/env vars from Actor.cpp

Author: ktoso

stdlib/public/Concurrency/Actor.cpp

@@ -352,12 +352,20 @@ bool swift_bincompat_useLegacyNonCrashingExecutorChecks() {
 
   // Potentially, override the platform detected mode, primarily used in tests.
 #if SWIFT_STDLIB_HAS_ENVIRON
-  if (const char *modeStr = runtime::environment::
-        concurrencyIsCurrentExecutorLegacyModeOverride()) {
-    if (strcmp(modeStr, "nocrash") == 0 || strcmp(modeStr, "legacy") == 0) {
-      return true;
-    } else if (strcmp(modeStr, "crash") == 0 || strcmp(modeStr, "swift6") == 0) {
-      return false; // don't use the legacy mode
+
+#if SWIFT_CONCURRENCY_EMBEDDED
+  const char *modeStr =
+      runtime::environment::concurrencyIsCurrentExecutorLegacyModeOverride();
+#else
+  // embedded does not have a runtime to read env variables from; ignore overrides
+  const char *modeStr = nullptr;
+#endif // SWIFT_CONCURRENCY_EMBEDDED
+
+  if (modeStr) {
+    if (strcmp(modeStr, "nocrash") == 0) {
+      useLegacyMode = true;
+    } else if (strcmp(modeStr, "crash") == 0) {
+      useLegacyMode = false;
     } // else, just use the platform detected mode
   } // no override, use the default mode
 #endif // SWIFT_STDLIB_HAS_ENVIRON