The postgresql tarball includes "libpg-fe.h", but it isn't found in any of
the RH7 postgresql RPMs.
Unless you go manually extract and install the libpg-fe.h from the
postgresql tarball you can't compile. The perl Postgresql DBD driver, and
the mod_auth_psql Apache authentication module among other software.
You're probably thinking of libpq-fe.h ("q", not "g") which is part of
postgresql-devel. The postgresql DBD builds just fine, and is part of the
current tree coming soon to a Rawhide near you.