This introduces a dependency on xxHash. Unfortunately, hashcat's
build system wants to rebuild xxHash from the source code located
in `<hashcat source root>/deps/git/xxHash`, a Git submodule whose
contents are not included in the source tarball we currently
download.
This could be fixed by either using a recursive git clone instead
a tarball download, or patching the build files to use an existing
installation of xxHash (i.e. the one already provided by Nix). I
believe the latter is preferable since it avoids the situation in
which the xxHash version used by hashcat is different to the xxHash
version used by all other Nix packages.
Fortunately, this situation has been greatly improved [1] since
release 5.0.0; the next release of hashcat should drop usage of
git submodules and provide better support for using existing
installations of dependencies.
[1] 4177e1ee28
