Try to map to General_Error where possible

core/os/os.odin

@@ -19,17 +19,51 @@ Platform_Error :: _Platform_Error
 #assert(size_of(Platform_Error) <= 4)
 #assert(intrinsics.type_has_nil(Platform_Error))
 
+General_Error :: enum u32 {
+	None,
+
+	Permission_Denied,
+	Exist,
+	Not_Exist,
+	Closed,
+
+	Timeout,
+
+	Broken_Pipe,
+
+	// Indicates that an attempt to retrieve a file's size was made, but the
+	// file doesn't have a size.
+	No_Size,
+
+	Invalid_File,
+	Invalid_Dir,
+	Invalid_Path,
+	Invalid_Callback,
+
+	Pattern_Has_Separator,
+
+	Unsupported,
+}
+
+
 Errno :: Error // alias for legacy use
 
 Error :: union #shared_nil {
+	General_Error,
 	io.Error,
 	runtime.Allocator_Error,
 	Platform_Error,
 }
-#assert(size_of(Error) <= 8)
+#assert(size_of(Error) == 8)
 
 ERROR_NONE :: Error{}
 
+@(require_results)
+is_platform_error :: proc(ferr: Error) -> (err: i32, ok: bool) {
+	v := ferr.(Platform_Error) or_else {}
+	return i32(v), i32(v) != 0
+}
+
 write_string :: proc(fd: Handle, str: string) -> (int, Errno) {
 	return write(fd, transmute([]byte)str)
 }