make Sys.command quote executing command on Windows (see #3402)

std/cpp/_std/Sys.hx

@@ -101,6 +101,7 @@
 			for( a in args )
 				cmd += " "+escapeArgument(a);
 		}
+		if (systemName() == "Windows") cmd = '"$cmd"';
 		return sys_command(cmd);
 	}
 

std/neko/_std/Sys.hx

@@ -111,6 +111,7 @@
 			for( a in args )
 				cmd += " "+escapeArgument(a);
 		}
+		if (systemName() == "Windows") cmd = '"$cmd"';
 		return sys_command(untyped cmd.__s);
 	}
 

std/php/_std/Sys.hx

@@ -89,6 +89,7 @@
 			for( a in args )
 				cmd += " "+escapeArgument(a);
 		}
+		if (systemName() == "Windows") cmd = '"$cmd"';
 		var result = 0;
 		untyped __call__("system", cmd, result);
 		return result;