Fixed linking against drat2er, and use drat2er (#2785)

Fixed linking against drat2er, and use drat2er (#2785)

* Fixed linking against drat2er/drat-trim

We have machinery for linking against drat2er. However, this machinery
didn't quite work because libdrat2er.a contains an (undefined) reference
to `run_drat_trim` from libdrat-trim.a.

Thus, when linking against libdrat2er.a, we also need to link against
libdrat-trim.a.

I made this change, and then tested it by actually calling a function
from the drat2er library (CheckAndConvertToLRAT) which relies on
`run_drat_trim`. Since this invocation compiles, we know that the
linking is working properly now.

* Combined the two libs, per Mathias

* drat2er configured gaurds