util: Use C99 flexible arrays

Use C99 flexible arrays instead of older style of one-element or
zero-length arrays.
It allows the compiler to generate errors when the flexible array does
not occur at the end in the structure.

Change-Id: I6b87680ec9f501945ae266ae4e4927efd2399d56
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76815
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/cbmem/cbmem.c

@@ -1116,7 +1116,7 @@ static void dump_tpm_log(void)
 struct cbmem_console {
 	u32 size;
 	u32 cursor;
-	u8  body[0];
+	u8  body[];
 }  __attribute__ ((__packed__));
 
 #define CBMC_CURSOR_MASK ((1 << 28) - 1)