tools/runqslower: Ensure own vmlinux.h is picked up first

Reorder include paths to ensure that runqslower sources are picking up
vmlinux.h, generated by runqslower's own Makefile. When runqslower is built
from selftests/bpf, due to current -I$(BPF_INCLUDE) -I$(OUTPUT) ordering, it
might pick up not-yet-complete vmlinux.h, generated by selftests Makefile,
which could lead to compilation errors like [0]. So ensure that -I$(OUTPUT)
goes first and rely on runqslower's Makefile own dependency chain to ensure
vmlinux.h is properly completed before source code relying on it is compiled.

  [0] https://travis-ci.org/github/libbpf/libbpf/jobs/677905925

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200422012407.176303-1-andriin@fb.com

tools/bpf/runqslower/Makefile

@@ -8,7 +8,7 @@ BPFTOOL ?= $(DEFAULT_BPFTOOL)
 LIBBPF_SRC := $(abspath ../../lib/bpf)
 BPFOBJ := $(OUTPUT)/libbpf.a
 BPF_INCLUDE := $(OUTPUT)
-INCLUDES := -I$(BPF_INCLUDE) -I$(OUTPUT) -I$(abspath ../../lib)
+INCLUDES := -I$(OUTPUT) -I$(BPF_INCLUDE) -I$(abspath ../../lib)
 CFLAGS := -g -Wall
 
 # Try to detect best kernel BTF source