Claiming "threadset clause" for implementation. (#126023)

threadset clause is part of free-agent threads. But, free-agent threads
also involves runtime implementation. So, added an separate entry for
threadset clause and claimed it for clang.

---------

Co-authored-by: Sunil Kuravinakop <[email protected]>

Author: SunilKuravinakop

clang/docs/OpenMPSupport.rst

@@ -364,6 +364,8 @@ implementation.
 +=============================================================+===========================+===========================+==========================================================================+
 | free-agent threads                                          | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
+| threadset clause                                            | :`worked on`              | :none:`unclaimed`         |                                                                          |
++-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | Recording of task graphs                                    | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | Parallel inductions                                         | :none:`unclaimed`         | :none:`unclaimed`         |                                                                          |