Hadrian: Inform Cabal of libgmp and libnuma paths

Previously the package database registration for integer-gmp and rts would lack knowledge of the paths of the system's libgmp and libnuma shared objects. In the make build system the latter was handled by rts/package.conf.in, which was generated by configure. I'm honestly not sure how the former was handled.

This branch fixes hadrian to ensure that the package registrations contain the locations of the system shared objects by informing Cabal of these locations.

When used with this ghc.nix patch this allows GHC's built under ghc.nix to be used outside of nix-shell.