systemtap: fix libdebuginfod auto detection logic

systemtap: fix libdebuginfod auto detection logic

Addresses an issue when systemtap is built in situation where debuginfod
is not part of DISTRO_FEATURES and latest SystemTap has problem of
auto detecting libdebuginfod library as it was reported by Martin
Jansa in [1].

[1] https://lists.openembedded.org/g/openembedded-core/message/192109?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Acreated%2C0%2Csystemtap%2C20%2C2%2C0%2C102987514

Signed-off-by: Victor Kamensky <victor.kamensky7@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>