In dll_crt0_0, both threadinterface->Init and sigproc_init allocate windows object handles using unpredictable memory regions, which may collide with dynamically loaded dlls when they were relocated.
THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cygwin documentation is available on the net at https://cygwin.com You might especially be interested in https://cygwin.com/faq/faq.html#faq.programming.building-cygwin