tools/resolve_btfids: Add /libsubcmd to .gitignore

Add libsubcmd to .gitignore, otherwise after compiling the kernel it
would result in the following:

    # bpf-next...bpf-next/master
    ?? tools/bpf/resolve_btfids/libsubcmd/

Signed-off-by: Rong Tao <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: Rtoax

tools/bpf/resolve_btfids/.gitignore

@@ -1,3 +1,4 @@
 /fixdep
 /resolve_btfids
 /libbpf/
+/libsubcmd/