detect when there are no fds to pass.
* dcrt0.cc (host_dependent_constants::init): Revert Sat Mar 18 01:32:04 2000
change.
(dll_crt0_1): Set "cygwin_finished_initializing" flag.
(dll_crt0): Don't perform memcpy if uptr is already set to internal structure.
(_dll_crt0): Remember location of programs envptr.
* dll_init.h (per_module, dll, dll_list): Revamp.
* dll_init.cc: Revamp. Use new classes.
* fork.cc (fork): Use new revamped dll, dll_list, and per_module stuff.
* environ.cc: Use __cygwin_environ throughout rather than the
user_data->envptr.
* exec.cc: Ditto.
* spawn.cc: Ditto.
* winsup.h: Declare update_envptrs, cygwin_finished_initializing.
* lib/_cygwin_crt0_common.cc (_cygwin_crt0_common): Revert previous change.
* lib/cygwin_attach_dll.cc (cygwin_attach_dll): Always pass in own per_process
structure or we end up overwriting information from the main program.
