bpf: Check CONFIG_BPF option for resolve_btfids

Currently all the resolve_btfids 'users' are under CONFIG_BPF
code, so if we have CONFIG_BPF disabled, resolve_btfids will
fail, because there's no data to resolve.

Disabling resolve_btfids if there's CONFIG_BPF disabled,
so we won't fail such builds.

Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200923185735.3048198-1-jolsa@kernel.org

Makefile

@@ -1084,13 +1084,15 @@ ifdef CONFIG_STACK_VALIDATION
   endif
 endif
 
+ifdef CONFIG_BPF
 ifdef CONFIG_DEBUG_INFO_BTF
   ifeq ($(has_libelf),1)
     resolve_btfids_target := tools/bpf/resolve_btfids FORCE
   else
     ERROR_RESOLVE_BTFIDS := 1
   endif
-endif
+endif # CONFIG_DEBUG_INFO_BTF
+endif # CONFIG_BPF
 
 PHONY += prepare0
 

scripts/link-vmlinux.sh

@@ -341,9 +341,9 @@ fi
 vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
 
 # fill in BTF IDs
-if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
-info BTFIDS vmlinux
-${RESOLVE_BTFIDS} vmlinux
+if [ -n "${CONFIG_DEBUG_INFO_BTF}" -a -n "${CONFIG_BPF}" ]; then
+	info BTFIDS vmlinux
+	${RESOLVE_BTFIDS} vmlinux
 fi
 
 if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then