During the discussion about the impact of adding counter to TCB
Mr anchao created a pthread mutex performance example:
https://github.com/apache/nuttx/pull/17468#issuecomment-3660925314
Because this example can exercise (not ideally) the pthread mutex
I decided to add it to apps/testing/sched, the program name will
be called "pmutexp" (because "pmp" is not a good name).
Signed-off-by: Alan C. Assis <acassis@gmail.com>
8cb7dd0694