Travis: add Windows build in a container

I expect this to become the default way to test Windows builds and
create installers on Travis. The idea is that instead of downloading the
pre-built MXE binaries we might as well use a container that has all
this installed and can be used locally to test if things fail on Travis;
which will allow us to have the exact same environment for testing
locally as runs on Travis.

At this point the container used is way too big - more effort needs to
be spent on shrinking it.

Right now this only deals with Subsurface and not with smtk2ssrf.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

scripts/windows-container/in-container-build.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+# this gets executed inside the container when building a Windows
+# installer on Travis
+#
+# working directory is assumed to be the directory including all the
+# source directories (subsurface, googlemaps, grantlee, etc)
+# in order to be compatible with the assumed layout in the MXE script, we
+# need to create the secondary build directory
+
+set -x
+set -e
+
+mkdir -p win32
+cd win32
+bash -ex ../subsurface/packaging/windows/mxe-based-build.sh installer
+
+# re-enable this when smtk2ssrf is figured out
+#bash -ex ${TRAVIS_BUILD_DIR}/packaging/windows/smtk2ssrf-mxe-build.sh -i