Fix up builds that are now too big for `develop` branch. (#12495)

keyboards/kbdfans/bella/rgb/rules.mk

@@ -23,3 +23,5 @@ AUDIO_ENABLE = no              # Audio output
 RGB_MATRIX_ENABLE = yes
 RGB_MATRIX_DRIVER = IS31FL3741
 NO_USB_STARTUP_CHECK = no      # Disable initialization only when usb is plugged in
+
+LTO_ENABLE = yes

keyboards/kbdfans/bella/rgb_iso/rules.mk

@@ -23,3 +23,5 @@ AUDIO_ENABLE = no              # Audio output
 RGB_MATRIX_ENABLE = yes
 RGB_MATRIX_DRIVER = IS31FL3741
 NO_USB_STARTUP_CHECK = no      # Disable initialization only when usb is plugged in
+
+LTO_ENABLE = yes

keyboards/mt64rgb/rules.mk

@@ -25,3 +25,5 @@ BLUETOOTH_ENABLE = no       # Enable Bluetooth
 AUDIO_ENABLE = no           # Audio output
 
 LAYOUTS = 64_ansi
+
+LTO_ENABLE = yes