gn: Switch to fetchzip for apple_apsl directory

The tarball from upstream seems to be generated on the fly, so the
output is not deterministic and using fetchzip makes this more reliable
as we have a recursively hashed output path without any of the
non-determinisms in tarballs.

Unfortunately, the build still fails on NixOS systems, because we need a
few more stuff in the build tree.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @matthewbauer, @stesie