Android: improve clang support
Summary:
Infer the toolchain we are using through cmake's detection of ranlib
instead of asking the user to fill it.
It's only used in androiddeployqt and cmake expects it to be version
"clang" for clang builds while androiddeployqt expects it to be "4.9".
Reviewers: Build System, Android, vkrause
Reviewed By: Android, vkrause
Subscribers: kde-frameworks-devel, kde-buildsystem
Tags: Frameworks, Build System
Differential Revision: https://phabricator.kde.org/D16930