* dcrt0.cc (_cygwin_testing): Define.
(_dll_crt0): Set _cygwin_testing if CYGWIN_TESTING environment variable exists.
Don't issue "conflicting versions" error if _cygwin_testing is true.
* shared.cc (shared_name): Use _cygwin_testing global rather than testing the
environment.
* syscalls.cc (_write): Remove debugging info.