Revert the reversion and go with implementation described in cgf-000017, with

some modifications.
* init.cc (dll_entry): Revert previous change.
* miscfuncs.cc: Include sigproc.h for exit_thread declaration.
* winsup.h (ExitThread): Define as 'exit_thread' to ensure no accidental use.
* sigproc.cc (exit_thread): New function.
(wait_sig): Handle __SIGTHREADEXIT case.  Don't just block rather than
returning from this function.
* sigproc.h (__SIGTHREADEXIT): New enum.
(exit_thread): Declare.
* sync.cc (muto::release): Accept a tls command-line argument.
* sync.h (muto::release): Accept a tls command-line parameter.  Default to
&_my_tls.
* cygerrno.h (__set_errno): Define as extern so that no function code is ever
emitted.
* cygserver_ipc.h (cygserver_ipc.h): Ditto.
* miscfuncs.h (transform_chars): Ditto.
* path.h (has_attribute): Ditto.
* security.h (privilege_luid): Ditto.
* winsup.h (flush_file_buffers): Ditto.

winsup/cygwin/security.h

@@ -354,13 +354,13 @@ extern cygpsid well_known_samba_unix_user_fake_sid;
 
 bool privilege_luid (const PWCHAR pname, LUID &luid, bool &high_integrity);
 
-inline BOOL
+extern inline BOOL
 well_known_sid_type (SID_NAME_USE type)
 {
   return type == SidTypeAlias || type == SidTypeWellKnownGroup;
 }
 
-inline BOOL
+extern inline BOOL
 legal_sid_type (SID_NAME_USE type)
 {
   return type == SidTypeUser  || type == SidTypeGroup