bpf, runqslower: include proper uapi/bpf.h

runqslower doesn't specify include path for uapi/bpf.h. This causes the
following warning:

In file included from runqslower.c:10:
.../tools/testing/selftests/bpf/tools/include/bpf/bpf.h:234:38:
warning: 'enum bpf_stats_type' declared inside parameter list will not
be visible outside of this definition or declaration
234 | LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);

Fix this by adding -I tools/includ/uapi to the Makefile.

Reported-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/bpf/runqslower/Makefile

···
 LIBBPF_SRC := $(abspath ../../lib/bpf)
 BPFOBJ := $(OUTPUT)/libbpf.a
 BPF_INCLUDE := $(OUTPUT)
-INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../lib)
+INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../lib)        \
+       -I$(abspath ../../include/uapi)
 CFLAGS := -g -Wall
 
 # Try to detect best kernel BTF source