Bindist `configure` should check for availability of `libgmp`
Currently configure does not check whether CC is able to link against libgmp if the bindist is configured to use the gmp integer backend.
Usually this isn't a problem since the ghc-pkg is a Haskell executable which runs during installation (which links against libgmp). This generally means that libgmp would certainly fail if it's not available at all on the system. However, in some cases the toolchain we configure against is unable to link against system libraries (e.g. in the case that we are using Anaconda's C toolchain). This means that configure can succeed yet installs a compiler that is unavailable.
The bindist configure script really should try linking against libgmp to ensure that the toolchain is usable.