tools/runqslower: Fix LDFLAGS and add LDLIBS support

Actually use previously defined LDFLAGS during build and add support for
LDLIBS to link extra standalone libraries e.g. 'argp' which is not provided
by musl libc.

Fixes: 585bf46 ("tools: runqslower: Add EXTRA_CFLAGS and EXTRA_LDFLAGS support")
Signed-off-by: Tony Ambardar <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Ilya Leoshkevich <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: guidosarducci

tools/bpf/runqslower/Makefile

@@ -15,6 +15,7 @@ INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../include/uapi)
 CFLAGS := -g -Wall $(CLANG_CROSS_FLAGS)
 CFLAGS += $(EXTRA_CFLAGS)
 LDFLAGS += $(EXTRA_LDFLAGS)
+LDLIBS += -lelf -lz
 
 # Try to detect best kernel BTF source
 KERNEL_REL := $(shell uname -r)
@@ -51,7 +52,7 @@ clean:
 libbpf_hdrs: $(BPFOBJ)
 
 $(OUTPUT)/runqslower: $(OUTPUT)/runqslower.o $(BPFOBJ)
-	$(QUIET_LINK)$(CC) $(CFLAGS) $^ -lelf -lz -o $@
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
 
 $(OUTPUT)/runqslower.o: runqslower.h $(OUTPUT)/runqslower.skel.h	      \
 			$(OUTPUT)/runqslower.bpf.o | libbpf_hdrs