A few more amd64 build changes.
Remove conflicting /MT /MTd flags.
Remove common7 from jamsh.bat PATH setting.
As a note, built a 64bit p4d.exe without smartheap. This port
is going to be some work. For starters, _get_osfhandle() now
has checks which fault the server. It's not clear on what it
will take to resolve this. I suspect MS has a bunch more issues
like this which must be addressed for the port.