correctly report "Mac" system name on OSX in macros (close HaxeFounda…

…tion#2612)

interp.ml

@@ -1637,11 +1637,25 @@ let std_lib =
 			Unix.chdir (vstring s);
 			VNull;
 		);
-		"sys_string", Fun0 (fun() ->
-			VString (match Sys.os_type with
-			| "Unix" -> "Linux"
-			| "Win32" | "Cygwin" -> "Windows"
-			| s -> s)
+		"sys_string", (
+			let cached_sys_name = ref None in
+			Fun0 (fun() ->
+				VString (match Sys.os_type with
+				| "Unix" ->
+					(match !cached_sys_name with
+					| Some n -> n
+					| None ->
+						let ic = Unix.open_process_in "uname" in
+						let uname = (match input_line ic with
+							| "Darwin" -> "Mac"
+							| n -> n
+						) in
+						close_in ic;
+						cached_sys_name := Some uname;
+						uname)
+				| "Win32" | "Cygwin" -> "Windows"
+				| s -> s)
+			)
 		);
 		"sys_is64", Fun0 (fun() ->
 			VBool (Sys.word_size = 64)