Taken from upstream subversion repository:

http://code.google.com/p/iksemel/source/detail?r=25

===================================================================
---
 configure.ac |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- iksemel-1.4.orig/configure.ac
+++ iksemel-1.4/configure.ac
@@ -43,11 +43,19 @@ AM_CONDITIONAL(DO_POSIX, test "x$defio"
 dnl Checks for library functions
 AC_SEARCH_LIBS(recv,socket)
 AC_CHECK_FUNCS(getopt_long)
 AC_CHECK_FUNCS(getaddrinfo)
 
-AM_PATH_LIBGNUTLS(,AC_DEFINE(HAVE_GNUTLS,,"Use libgnutls"))
+dnl Check GNU TLS
+PKG_CHECK_MODULES(GNUTLS, gnutls >= 2.0.0, have_gnutls=yes, have_gnutls=no)
+if test "x$have_gnutls" = "xyes"; then
+  LIBGNUTLS_CFLAGS="$GNUTLS_CFLAGS"
+  LIBGNUTLS_LIBS="$GNUTLS_LIBS"
+  AC_SUBST(LIBGNUTLS_CFLAGS)
+  AC_SUBST(LIBGNUTLS_LIBS)
+  AC_DEFINE(HAVE_GNUTLS, 1, [whether to use GnuTSL support.])
+fi
 
 dnl Check -Wall flag of GCC
 if test "x$GCC" = "xyes"; then
   if test -z "`echo "$CFLAGS" | grep "\-Wall" 2> /dev/null`" ; then
     CFLAGS="$CFLAGS -Wall"