A Configure Patch for new cygwin

["Teluhiko HILANO" <hilano@aqu.bekkoame.ne.jp>]

I'm using PARI under cygwin.

Recently cygwin's version is up and the directory tree is changed.
I installed it on C:\ and the following patch to Configure works well to 
PARI static version with gnu readline.

I have never succeed to make PARI dynamic version on cygwin
because some global variable cannot resolved. 

388,391c388
<         cygtop=/usr/${arch}-pc-cygwin
<         if test ! -d $cygtop; then
<           echo ..."I could not find Cygwin top directory" >&2
<         fi
---
>         echo ..."I could not find Cygwin top directory" >&2
402d398
<  	$cygtop/lib\
-------------------------------------------------
      Teluhiko HILANO(hilano@bekkoame.ne.jp)
                 (hilano@gen.kanagawa-it.ac.jp)
                 (RXF13157@nifty.ne.jp)
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