Fix process_unicode_common.c being included twice

build_keyboard.mk

@@ -176,22 +176,26 @@ endif
 
 ifeq ($(strip $(UCIS_ENABLE)), yes)
     OPT_DEFS += -DUCIS_ENABLE
-    SRC += $(QUANTUM_DIR)/process_keycode/process_unicode_common.c
+    UNICODE_COMMON = yes
     SRC += $(QUANTUM_DIR)/process_keycode/process_ucis.c
 endif
 
 ifeq ($(strip $(UNICODEMAP_ENABLE)), yes)
     OPT_DEFS += -DUNICODEMAP_ENABLE
-    SRC += $(QUANTUM_DIR)/process_keycode/process_unicode_common.c
+    UNICODE_COMMON = yes
     SRC += $(QUANTUM_DIR)/process_keycode/process_unicodemap.c
 endif
 
 ifeq ($(strip $(UNICODE_ENABLE)), yes)
     OPT_DEFS += -DUNICODE_ENABLE
-    SRC += $(QUANTUM_DIR)/process_keycode/process_unicode_common.c
+    UNICODE_COMMON = yes
     SRC += $(QUANTUM_DIR)/process_keycode/process_unicode.c
 endif
 
+ifeq ($(strip $(UNICODE_COMMON)), yes)
+    SRC += $(QUANTUM_DIR)/process_keycode/process_unicode_common.c
+endif
+
 ifeq ($(strip $(RGBLIGHT_ENABLE)), yes)
     OPT_DEFS += -DRGBLIGHT_ENABLE
     SRC += $(QUANTUM_DIR)/light_ws2812.c