Have clang ignore the code in bootloader_size.c

tmk_core/common/avr/bootloader_size.c

@@ -16,5 +16,6 @@
 #include <avr/io.h>
 #include <avr/boot.h>
 
+// clang-format off
 // this is not valid C - it's for computing the size available on the chip
-AVR_SIZE: FLASHEND + 1 - BOOTLOADER_SIZE
+AVR_SIZE: FLASHEND + 1 - BOOTLOADER_SIZE