Make tests link to the library

[janden]

Right now, they link directly to the raw object files. Having the tests link to the library would more closely mimic end-user behavior.

[MelodyShih]

I have in mind that the end users can use the codes under cufinufft/examples to see how the library can be used, so it is probably not necessary for test codes to closely mimic the end-user behavior?

[janden]

I guess what I'm worried about not catching errors in the build process (due to linking the library) in the automated tests (once we get those up and running).