Fix parallel build of KLU

[thasti]

Here's another minor one (I'm trying to get this packaged for Arch Linux).

When running make all with a multi-CPU option (-j8 in my case), the KLU patch fails to be applied as the patch and unpack targets are evaluated simultaneously - leading to a race condition of unpacking not having finished before patching is attempted. Putting unpack (though not a true file target) as a dependency of patch fixed that.

[thasti]

On closer inspection, it looks like the build system generally does not cope well with the -j option in various places (installation being one of them). In many places, the actual dependencies don't appear to be modeled, especially when archives are part of the build.
In case I were to look at this more systematically, would you be accepting a larger patch set (and should we move the associated discussion to a Github issue instead)?