There's App::Info and Alien for detecting non-Perl dependencies, but someone would have to code up the libgmp parts explicitly.
Well, Alien mainly exists as an idea in Arthur Bergman's head. (Maybe he has been taken over by an alien?). It's goal is to provide packages for installing non-Perl dependencies.
App::Info, OTOH, is designed to provide a unified interface for determining if an external dependency is installed on the local system, and if so, information about it (version number, binary location, etc.). Check out App::Info::Lib::Expat for examples of how to create your own subclass, and this link for instructions on subclassing:
http://search.cpan.org/dist/App-Info/lib/App/Info.pm#SUBCLASSING
Cheers,
David
