make install in winsup

[DJ Delorie]

> IIRC, used to be, the DLL was installed as new-cygwin1.dll. I'm

The dll is *created* that way, because it's created in multiple steps
and we don't want any cygwin programs seeing a partial cygwin1.dll and
crashing.  If we *installed* it as new-*, it wouldn't work (the
programs look for cygwin1.dll, not new-cygwin1.dll, and *who* is going
to rename it after the install?)