Currently files to install in runtime/ is detected by recursive glob
pattern which has two problems:
- cmake needs to do a of work at config time and
build/runtime/cmake_install.cmake becomes HUGE (2.5MB, biggest config file)
- we need to explicitly specify each file suffix used in the entire
runtime, which is duplication of information.
These globs specify every single file in a subdirectory.
Thus, we can just install every runtime/ subdirectory as a single
install command. Furthermore, at the top-level, only .vim and .lua files
need to be installed.
Further possible refactor: we could move files which does not belong
in $PREFIX/runtime out of $REPO/runtime. Then runtime could be installed
with a single install_helper(DIRECTORY ...) command.