build emacs and gnutls not found

The error message tells you two ways in which to solve your problem.

1. Install the gnutls development package. You can find it by doing: apt-cache search 'libgnutls.*-dev', and then install it with apt-get.
2. Link without gnutls, a la ./config --prefix=/usr/local/emacs --with-gnutls=no

The only thing that worked for me was installing pkg-config.

Fixed on CentOS:

yum install gnutls-devel