Remove some obviously useless tests (and fix the others so they build).

Some of these tests are stupid (hello_world.cpp), others are already replaced
by more complete tests in bionic (test_cpu_set.cpp).

Change-Id: Ie6d2723b049b4e9bb1b98ae0166be2c19551fdd0
Merge "Remove some obviously useless tests (and fix the others so they build)."
Remove obsolete semaphore tests.

Change-Id: I96d0dbbb8d3482a19ce33e389971451fa630c84a
Remove a useless pthread_join test.

Change-Id: Ie37deaf62338e541434115d6b7ae748cc38b85a3
Merge "Remove obsolete semaphore tests."
Merge "Remove a useless pthread_join test."