Don't strip libgmp.a. (But perhaps --strip-unneeded or something
would be harmless.)

PS. The configure script looks for __gmpz_fdiv_qr, but gmp that I have
installed uses the name mpz_fdiv_qr and is thus not being found. (Also
it is dynamically linked, where ghc's gmp is only statically linked.)
I guess that configure should check for either name.