The cmake files were moved upstream [0] and the build now fails because it
silently falls back to the GNU Makefile:
install: cannot change permissions of '/usr/local/bin/': Operation not permitted
Point to the new location and set PKG_TOOLCHAIN explicitely to "cmake", which
would have caugth this issue:
CMake Error: The source directory "/tmp/libreelec/build.LibreELEC-H6.arm-9.80-devel/build/lz4-1.9.3/contrib/cmake_unofficial" does not exist.
Specify --help for usage, or press the help button on the CMake GUI.
FAILURE: ./scripts/build lz4:host during configure_host (default)
[0] 31d477db07
Move variable assignments into configure_package() if the assignments
depend on variables initialised after the package is sourced, ie.
$PKG_BUILD, $PKG_SOURCE_NAME etc.
