Include an Android CI

It uses the following image:
https://phabricator.kde.org/source/sysadmin-ci-tooling/browse/master/system-images/android/sdk/Dockerfile-clang

The one we are using now as kdeorg/android-sdk is still using GCC which
can't compile poppler master (it can compile last stable version, but
new features are used now and it can't cope).
KDE will start using this clang version when Qt 5.12 releases and we
know there's no major regressions, but poppler can already start doing
so now.

It only checks that poppler builds correctly, doesn't execute anything.
6 jobs for androidci in 8 minutes and 27 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #46586
build

00:04:41

passed #46591
build_android

00:01:02

passed #46587
build_clang_libcpp

00:04:00

passed #46590
build_clazy

00:03:53

passed #46588
build_gcc_49

00:08:27

passed #46589
build_mingw64_fedora

00:02:51