BLD: Tell fortran compiler Cygwin doesn't support rpath.

Cygwin inherits Windows's lack of RPATH.

Author: DWesl

numpy/distutils/fcompiler/gnu.py

@@ -247,7 +247,7 @@ def get_flags_arch(self):
         return []
 
     def runtime_library_dir_option(self, dir):
-        if sys.platform == 'win32':
+        if sys.platform == 'win32' or sys.platform == 'cygwin':
             # Linux/Solaris/Unix support RPATH, Windows does not
             raise NotImplementedError