Building Exim against Heimdal 1.5, heimdal-gssapi.pc was needed.
There's been a major version bump in Heimdal, and against 7.1 that
doesn't work; using heimdal-krb5.pc fails on missing `gss_*` functions.
I can find no build documentation for Heimdal which describes what
should be needed. heimdal-gssapi.pc does reference heimdal-krb5.pc
in `Requires.private` but it's not being used by FreeBSD pkgconf in
such a way that it's available when building on FreeBSD 10.3.
Fortunately, our `*_PC` logic works with multiple packages listed,
so provide that example.
# AUTH_GSASL_PC=libgsasl
# AUTH_HEIMDAL_GSSAPI=yes
# AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
+# AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi heimdal-krb5
# AUTH_PLAINTEXT=yes
# AUTH_SPA=yes
# AUTH_TLS=yes
+# Heimdal through 1.5 required pkg-config 'heimdal-gssapi'; Heimdal 7.1
+# requires multiple pkg-config files to work with Exim, so the second example
+# above is needed.
#------------------------------------------------------------------------------
# If you specified AUTH_CYRUS_SASL above, you should ensure that you have the