[Keymap] fix sigma keymaps build (#8427)

handle unicode input properly.

keyboards/converter/sun_usb/type5/keymaps/sigma/rules.mk

@@ -1 +1,2 @@
 BOOTLOADER = halfkay
+UNICODE_ENABLE = yes

users/sigma/sigma.c

@@ -64,6 +64,7 @@ void led_set_keymap(uint8_t usb_led) {}
 void set_os(uint8_t os) {
   runtime_userspace_config.os_target = os;
 
+#if defined(UNICODE_ENABLE) || defined(UNICODEMAP_ENABLE) || defined(UCIS_ENABLE)
   switch (os) {
   case _OS_MACOS:
     set_unicode_input_mode(UC_OSX);
@@ -75,6 +76,7 @@ void set_os(uint8_t os) {
     set_unicode_input_mode(UC_WIN);
     break;
   }
+#endif
 }
 
 void matrix_init_user(void) {