Revert 3ea4e6f7b85f: Force autoreconf for mpfr

It breaks on my machine. Revert until we find the exact cause leading to
the initial patch, and we come up with a patch that properly fixes it.

 reporter_name="Harold Grovesteen"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

 reporter_comment=""