You can start by checking whether you have libgmp and whether it has the referenced symbol, e.g. on my machine, there's a /usr/lib64/libgmp.a, and I get this:
$ nm /usr/lib64/libgmp.a | grep mpz_powm_sec
0000000000000000 T __gmpz_powm_sec
I'm not sure what the relationship is between __gmpz_powm_sec and mpz_powm_sec, though it may be just some naming convention.
Without knowing much about various versions of GHC or libgmp, I think it's possible that newer GHC requires newer libgmp that has this symbol and you have an older libgmp.
Josh