If you want to find the gnutls library in other projects
using autoconf/aclocal, put in your 

aclocal.m4:
 include(gnutls.m4)

configure.in:
 AM_PATH_GNUTLS( 0.2.0,, AC_MSG_ERROR[[*** gnutls was not found]]))


these macros define GNUTLS_LIBS and GNUTLS_CFLAGS.