Issue #16588: Silence unused-but-set warnings in Python/thread_pthread.h

diff --cc Misc/NEWS
index 11a313f6aaef7cc284c7b54b057e7b67fd535ec0,291fb4c1ca23ee60af447d56eb30581e2f61e87f..3b38db7a981d8a087d974b9b6d082beb7d122aaf
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -10,9 -12,8 +10,11 @@@ What's New in Python 3.4.0 Alpha 1
  Core and Builtins
  -----------------
  
+ - Issue #16588: Silence unused-but-set warnings in Python/thread_pthread
+ 
 +- Issue #16592: stringlib_bytes_join doesn't raise MemoryError on allocation
 +  failure.
 +
  - Issue #16546: Fix: ast.YieldFrom argument is now mandatory.
  
  - Issue #16514: Fix regression causing a traceback when sys.path[0] is None