Add patch for strange libical linker error

* Makefile.am (EXTRA_DIST): Add patch.
* patches/libical/workaround-weird-mingw-10.0.0-issue.patch:
New.

This fixes an issue that one some distros opendir from mingw-crt
somehow pulls in libssp. Since we believe that this is an
upstream bug and the alternative code in libical looks fine
we disable to use of opendir for now.