www-servers/lighttpd-1.4.55 builds and installs just fine without dev-libs/libgamin installed. The latter depends on dev-lang/python:2.7 and was the only package remaining on my system with that dependency.
The Lighttpd ebuild should lose the BDEPEND on dev-libs/libgamin so Python 2.7 can be cut loose.
libgamin does not depend on python2.7, unless you requested it to. So this potential lighttpd bug does in no way block the python stuff (there's a separate bug for libgamin on that).
As for this bug, it seems it does need libgamin (or rather virtual/fam), but that should only be with USE=fam. But maybe something in autotools could also be wonky, and fam.h check is unconditional. That's for the maintainer to look into.