[RFA] enable dynamic (thread safe) reents

[Thomas Pfaff]

Thomas Pfaff wrote:
> 2003-05-16  Thomas Pfaff  <tpfaff@gmx.net>
> 
> 	* include/cygwin/config.h (__DYNAMIC_REENT__): Define.
> 	* include/cygwin/version.h: Bump API minor version.
> 	* cygwin.din: Export __getreent
> 	* cygerrno.h: Include errno.h.
> 	Fix places where _impure_ptr is used directly to store the errno
> 	value.

	* debug.cc (__set_errno): Ditto.

> 	* errno.cc: Remove _RRENT_ONLY define to get errno.cc compiled.
> 	* signal.cc: Rename _reent_clib to _REENT throughout.
> 	* thread.h (reent_clib): Remove prototype.
> 	* thread.cc (reent_clib): Rename reent_clib to __getreent.
> 	Return _impure_ptr until MTinterface is initialized.
> 	(reent_winsup): Fix a possible SEGV when _r == NULL.
> 	Return NULL instead.
> 	* MTinterface::fixup_after_fork: Switch reent back to
>       _impure_ptr
> 	to keep signal handling running when fork is called from a
>       thread other than the mainthread.