swift: export the `objc_retainAutoReleaseReturnValue`
Export the stub that we provide for swift programs on Windows.  This is
used by CoreFoundation and thus is needed for the Foundation port on
Windows.
#include <dispatch/dispatch.h>
#include <stdio.h>
+#if defined(__ELF__) || defined(__MACH__) || defined(__WASM__)
#define DISPATCH_RUNTIME_STDLIB_INTERFACE __attribute__((__visibility__("default")))
+#else
+#define DISPATCH_RUNTIME_STDLIB_INTERFACE __declspec(dllexport)
+#endif
#if USE_OBJC
@protocol OS_dispatch_source;
@@ -54,6 +58,7 @@ static void _dispatch_overlay_constructor() {
#endif /* USE_OBJC */
#if !USE_OBJC
+DISPATCH_RUNTIME_STDLIB_INTERFACE
extern "C" void * objc_retainAutoreleasedReturnValue(void *obj);
#endif
