I don't think the patch, cygwin-smaller.diff, is correct. The value of
static_lib_extension needs to remain ".a". Otherwise, shared
extensions attempting to build against a library that only offers a
static version will fail to link.
AFAICT, Cygwin needs a concept that is not currently supported by
distutils -- the ability to specify a shared library *link* extension
(i.e., ".dll.a") which is different from the shared library extension
(i.e., ".dll"). On Unix they are the same (e.g., ".so"), but on Cygwin
they are different because of how Windows handles DLLs -- import
library versus DLL.