MPC (http://www.multiprecision.org/) is the complex number version of
MPFR and will be required in the future for gcc-4.5. While that is
still a while off, I want to add this to [testing] in the mean time to
allow easier testing of future gcc builds. Given the clash of names
with the other mpc, I have been naming this libmpc as has been the
strategy in Debian.