Enable cephes on FreeBSD and disable it on Cygwin

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/9543">trac #9543</a>.

Spkg diff, for review only.

Reported by: pjeremy

Component: FreeBSD

CC: mhansen,, jpflori

Report Upstream: N/A

Authors: Peter Jeremy, Jean-Pierre Flori

Dependencies: 

Work issues: 

Reviewers: Stephen Montgomery-Smith, Karl-Dieter Crisman

Merged in: sage-5.6.rc0

Attachments: <ol><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/9543/cephes-2.8.p0.diff">cephes-2.8.p0.diff: Spkg diff, for review only.</a> by jpflori at 20130108T14:17:28</li><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/9543/cephes-2.8.p1.diff">cephes-2.8.p1.diff: Spkg diff, for review only.</a> by jpflori at 20130109T15:26:55</li></ol>