[stdlib] StdlibUnittestFoundationExtras: fix warnings

Author: lorentey

stdlib/private/StdlibUnittestFoundationExtras/StdlibUnittestFoundationExtras.swift

@@ -72,7 +72,7 @@ public func withOverriddenLocaleCurrentLocale<Result>(
 public func autoreleasepoolIfUnoptimizedReturnAutoreleased(
   invoking body: () -> Void
 ) {
-#if arch(i386) && (os(iOS) || os(watchOS))
+#if targetEnvironment(simulator) && arch(i386) && (os(iOS) || os(watchOS))
   autoreleasepool(invoking: body)
 #else
   body()