Fix polymorphic element types usage; Empty union as opaque type

core/_preload.odin

@@ -314,7 +314,6 @@ copy :: proc(dst, src: $T/[]$E) -> int #cc_contextless {
 }
 
 
-
 append :: proc(array: ^$T/[]$E, args: ...E) -> int #cc_contextless {
 	if array == nil do return 0;
 
@@ -356,6 +355,19 @@ append :: proc(array: ^$T/[dynamic]$E, args: ...E) -> int {
 	return len(array);
 }
 
+append :: proc(array: ^$T/[]u8, args: ...string) -> int {
+	for arg in args {
+		append(array, ...cast([]u8)arg);
+	}
+	return len(array);
+}
+append :: proc(array: ^$T/[dynamic]u8, args: ...string) -> int {
+	for arg in args {
+		append(array, ...cast([]u8)arg);
+	}
+	return len(array);
+}
+
 pop :: proc(array: ^$T/[]$E) -> E #cc_contextless {
 	if array == nil do return E{};
 	assert(len(array) > 0);