libc/glibc: print name of skipped addon

When trying to extract an already present (aka bundled) addon,
print the name of that addon, for clarity, and to help analyse
the build.log post-mortem.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

 reporter_name="Thomas Petazzoni"

 reporter_url="http://www.free-electrons.com/"

 reporter_comment="Very basic testing only"