packit: Re-enable and fix dist build

libssh, pcp, and polkit are not installed in the Packit sandcastle
container, and they are not necessary for merely building a dist
tarball. Disable these optional features.

Explicitly specify an invalid systemd unit dir to skip the pkg-config
query.

krb, systemd, and json-glib development files are also not currently
available in sandcastle, so point configure to some mock pkg-config
files to get past ./configure checks and still be able to run `make
dist`.

Re-enable Packit tests which were disabled in commit c4908fe050.

packit.yaml

@@ -6,7 +6,7 @@ actions:
     - sh -c 'sed "s/%{npm-version:.*}/0/" tools/cockpit.spec > cockpit.spec'
     # this is being triggered immediately on a pull_request event; wait for
     # build-dist.yml to generate the dist tarball
-    - test/make_dist.py --wait
+    - env AUTOGEN_CONFIGURE_ARGS='--disable-polkit --disable-ssh --disable-pcp --disable-doc --with-systemdunitdir=/invalid CPPFLAGS=-Itools/mock-build-env PKG_CONFIG_PATH=$PWD/tools/mock-build-env' test/make_dist.py --wait
     # packit service insists of a single line of output
     - sh -c 'ls cockpit-*.tar.xz'
 jobs:

tools/mock-build-env/README.md

@@ -0,0 +1,5 @@
+These are some stub pkg-config and include files that allow us to run
+`make dist` in a restricted build environment without the regular build
+dependencies, in particular [Packit](https://packit.dev/)'s [sandcastle container](https://github.com/packit/sandcastle).
+
+These are used in [packit.yaml](./packit.yaml).

tools/mock-build-env/gnutls.pc

@@ -0,0 +1,3 @@
+Name: GnuTLS
+Description: Mock PC for gnutls
+Version: 3.6.12.fake

tools/mock-build-env/json-glib-1.0.pc

@@ -0,0 +1,3 @@
+Name: JSON-GLib
+Description: Mock PC for json-glib
+Version: 1.6.fake

tools/mock-build-env/krb5-gssapi.pc

@@ -0,0 +1,3 @@
+Name: krb5-gssapi
+Description: Mock PC for krb5-gssapi
+Version: 1.18.2.fake

tools/mock-build-env/krb5.pc

@@ -0,0 +1,3 @@
+Name: krb5
+Description: Fake PC for krb5
+Version: 1.18.2.fake

tools/mock-build-env/security/pam_appl.h

@@ -0,0 +1 @@
+/* stub header to satisfy configure check */