Note that as part of this commit semaphore.cpp is excluded from the
DynamicLoader, as the dynamic loader does not build with pthread.cpp
which semaphore.cpp uses.
This helps ensure random pointers are not passed in as semaphores, but
more importantly once named semaphores are implemented, this will
ensure that random files are not used as semaphores.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
