NEWS: add entries for rb_waitpid and timer-thread [ci skip]

Some of these changes may affect debugging and tracing tools

[Bug #14867] [ruby-core:88199] [Misc #14937]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64522 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -345,6 +345,8 @@ sufficient information, see the ChangeLog file or Redmine
       very few optimizations are implemented.  So it's not ready for
       benchmarking Ruby's JIT performance yet. It's known that current JIT
       enablement makes Rails application slower for now.
+    * rb_waitpid reimplemented on Unix-like platforms to maintain
+      compatibility [Bug #14867]
 
 * VM generator script renewal; makes the generated VM more optimized.
   [GH-1779]
@@ -352,6 +354,8 @@ sufficient information, see the ChangeLog file or Redmine
 * Thread cache enabled for pthreads platforms (for `Thread.new` and
   `Thread.start`).  [Feature #14757]
 
+* timer thread is eliminated for platforms with POSIX timers [Misc #14937]
+
 ### Miscellaneous changes
 
 * On macOS, shared libraries no longer include a full version number of ruby