ebpf: fix harmless warning while loading eBPF prog

simple add -fno-asynchronous-unwind-tables to CFLAGS in order to get ride of
warning while libbpf is loading eBPF prog:

libbpf: elf: skipping unrecognized data section(32) .eh_frame
libbpf: elf: skipping relo section(33) .rel.eh_frame for section(32) .eh_frame

src/bpf/Makefile

@@ -77,5 +77,6 @@ $(TARGETS): %.bpf: %.c
 	    -Wno-tautological-compare \
 	    -Wno-unknown-warning-option \
 	    -Wno-address-of-packed-member \
+	    -fno-asynchronous-unwind-tables \
 	    -O2 -emit-llvm -g -c $< -o ${@:.bpf=.ll}
 	@$(LLC) -march=bpf -filetype=obj -o $(BIN)/$@ ${@:.bpf=.ll}