I can't build lame-3.99.tar.gz from SourceForge
(sha1sum 6c311fb9c7849048fc29ffe150ac39af03f57504 )
with the option "--enable-mp3rtp". Obviously frontend/rtp.h is missing in this tarball. CVS doesn't indicate that that file was ever removed, so it should be in.
I grabbed the file from CVS, and lame built successfully.
Thanks Moritz!
The missing file rtp.h is now added to the tarball.