libbpf-tools: Add flag -Werror=undef

Author: ShawnZhong

libbpf-tools/Makefile

@@ -9,8 +9,8 @@ LIBBPF_SRC := $(abspath ../src/cc/libbpf/src)
 LIBBPF_OBJ := $(abspath $(OUTPUT)/libbpf.a)
 LIBBLAZESYM_SRC := $(abspath blazesym/target/release/libblazesym.a)
 INCLUDES := -I$(OUTPUT) -I../src/cc/libbpf/include/uapi
-CFLAGS := -g -O2 -Wall -Wmissing-field-initializers -Werror
-BPFCFLAGS := -g -O2 -Wall
+CFLAGS := -g -O2 -Wall -Wmissing-field-initializers -Werror -Werror=undef
+BPFCFLAGS := -g -O2 -Wall -Werror=undef
 INSTALL ?= install
 prefix ?= /usr/local
 bindir := $(prefix)/bin

libbpf-tools/memleak.c

@@ -685,7 +685,7 @@ pid_t fork_sync_exec(const char *command, int fd)
 	return pid;
 }
 
-#if USE_BLAZESYM
+#ifdef USE_BLAZESYM
 void print_stack_frame_by_blazesym(size_t frame, uint64_t addr, const blazesym_csym *sym)
 {
 	if (!sym)