Begin mapping os.Error in the rest of the codebase

core/flags/internal_rtti.odin

@@ -254,7 +254,7 @@ parse_and_set_pointer_by_named_type :: proc(ptr: rawptr, str: string, data_type:
 		}
 
 		handle, errno := os.open(str, mode, perms)
-		if errno != 0 {
+		if errno != nil {
 			// NOTE(Feoramund): os.Error is system-dependent, and there's
 			// currently no good way to translate them all into strings.
 			//