Fix a few problems with the AMD64 merge.
* Fix genesis of double-floats on 32-bit little-endian platforms.
* Remove Makefile kludge for forcing shared libraries in contribs
to use the 32-bit mode on AMD64.
* Remove extra argument to MY-MAKE-WIRED-TN in x86-64/c-call.lisp
(prevented using CMUCL as host, since it gives a full warning).
* Add a NEWS entry for the new port.