There is a build problem with Lib/GSL/SF under
cygwin which I found when I last reported on cygwin.
I did not have time to fix the C code, but a
workaround fix for cygwin was to have the GSL/SF
build skipped if
(1) WITH_GSL was undef, and
(2) the OS was cygwin.
I think that does the right thing until the specific
code/linking under SF/coulomb can be fixed.