[Bug bootstrap] [4.1 regression] Build fails on Cygwin

[François-Xavier Coudert]

Patches needed to build on mingw32 include
http://gcc.gnu.org/ml/gcc-patches/2005-08/msg00009.html and
http://gcc.gnu.org/ml/gcc-patches/2005-08/msg00097.html . The first
one contains the fix to your problem, the second one is the latest
version of the patch to fix dllimport.

However, on mingw32, this is not enough to build (see PR 23210, for example).

FX