Let iconv build on Cygwin without installing Cygwin libiconv package

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/13912">trac #13912</a>.

Spkg diff, for review only.

Reported by: jpflori

Component: packages

CC: kcrisman

Report Upstream: N/A

Authors: Jean-Pierre Flori

Dependencies: 

Work issues: 

Reviewers: Jeroen Demeyer

Merged in: sage-5.7.beta0

Attachments: <ol><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/13912/iconv-1.13.1.p4.diff">iconv-1.13.1.p4.diff: Spkg diff, for review only.</a> by jpflori at 20130113T13:25:26</li></ol>