bpftool: Add -Wformat-signedness flag to detect format errors

This commit adds the -Wformat-signedness compiler flag to detect and
prevent printf format errors, where signed or unsigned types are
mismatched with format specifiers. This helps to catch potential issues at
compile-time, ensuring that our code is more robust and reliable. With
this flag, the compiler will now warn about incorrect format strings, such
as using %d with unsigned types or %u with signed types.

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250311112809.81901-2-jiayuan.chen@linux.dev

Author: mrpre

tools/bpf/bpftool/Makefile

@@ -71,7 +71,12 @@ prefix ?= /usr/local
 bash_compdir ?= /usr/share/bash-completion/completions
 
 CFLAGS += -O2
-CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers
+CFLAGS += -W
+CFLAGS += -Wall
+CFLAGS += -Wextra
+CFLAGS += -Wformat-signedness
+CFLAGS += -Wno-unused-parameter
+CFLAGS += -Wno-missing-field-initializers
 CFLAGS += $(filter-out -Wswitch-enum -Wnested-externs,$(EXTRA_WARNINGS))
 CFLAGS += -DPACKAGE='"bpftool"' -D__EXPORTED_HEADERS__ \
 	-I$(or $(OUTPUT),.) \