Fixes for using system libraries

I found these errors while compiling `libswiftnav` against my system libraries instead of the bundled ones.

First, both `libswiftnav.so` and `liblapacke.so` reference symbols from `liblapack.so`, it just doesn't cause an error until you try to link an executable against `libswiftnav.so`.

Second, `f2c.h` is not necessarily included by `clapack`, so explicitly including `f2c.h` whenever using definitions from it (ie the `integer` type) is necessary.

Thanks!