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.
(dll_crt0_1): Eliminate user_data initialization.
(dll_crt0): Set up impure_ptr_ptr for older executables.
(cygwin_dll_init): Eliminate user_data initializations.
(__api_fatal): Don't check for user_data initialization.
* dll_init.cc (struct dll): Store entire contents of per_process rather than
just a pointer.
(add): Ditto.
(initOneDll): Don't check for user_data initialization.
(DllList::recordDll): Store contents of per_process argument.
(DllList::detachDll): Pass address of per_process field.
(DllList::initAll): Ditto.
(DllList::doGlobalDestructorsOfDlls): Ditto.
(DllListIterator::operator *): Ditto.
(dll_dllcrt0): Default to __cygwin_user_data if arg is NULL.
* include/sys/cygwin.h: Reorganize per_process to eliminate obsolete fields and
accomodate new way of initializing.
* lib/_cygwin_crt0_common: Initialize _impure_ptr from
__cygwin_user_data.impure_ptr.
