It's now in its own repo

In particular, we need:
    * configure.ac: Add -no-undefined for both 32- and 64-bit x86
      windows-like hosts.
for Win64

We now use the binary that has come with GHC distributions for some
time, rather than the MSYS binary that requires extra DLLs.

This includes bin/msys-1.0.dll, which bin/perl.exe needs.