Android: Fix small build issues

Summary:
KDocTools isn't necessary for kstars_lite
Make sure we error when building on a system that doesn't have dos2unix,
makes finding what to do easier.
Prefer checking if we're on android using __ANDROID__ which is the one
defined by the NDK. See
/opt/android-ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-gcc -E -dM - < /dev/null | grep -i android
Define strings as QStrings, newer ki18n chokes on literals.
Use qRound instead of std::round, just works, maybe it needed to add an

Test Plan: Built it with KDE's binary-factory docker image, if this lands we'll get to include kstars in the nightly builds.

Reviewers: KDE Edu, mutlaqja, ckertesz

Reviewed By: ckertesz

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D14189