align _END label, add ALIGN directive to assembler

- fixes failing memory allocator when _END label is not aligned

pcomp/emit.pas

@@ -324,7 +324,9 @@ begin
 	rewindStringList(usedUnits);
 	while nextStringListItem(usedUnits, unitName) do
 		emitInclude(unitName + UnitSuffix2);
-
+	(* _END label needs to be word-aligned because
+		it is used as the start of the heap *)
+	emitIns('.ALIGN');
 	emitLabelRaw('_END');
 end;