tools/build: Add bpftool-skeletons feature test

Add bpftool-skeletons feature test, testing the presence of a bpftool
capable of generating skeletons.

This is to be used for tools that do not require building their own
bootstrap bpftool from the kernel source tree.

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Link: https://lore.kernel.org/20250218145859.27762-3-tglozar@redhat.com


Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>