Use install_symlink() in Meson versions that support it, or a script
with similar invocation in versions that do not. This will make it
straightforward to migrate to install_symlink() when we drop support
for Meson versions older than 0.61.0.
Based on an implementation in the game-data-packager package, which used
a shell script.
Signed-off-by: Simon McVittie <smcv@collabora.com>
