The class does not have any virtual methods, and thus the (debug-only)
destructor does not need to be virtual.

Bionic doesn't have the SYS_* macros.

Use it if it exists, but don't insist if the C library is poor
(e.g. Bionic/Android).

Bionic's pthread declarations are non-literal.

Allows the kernel to combine timer wakeups with other processes,
reducing power usage.

pthread_setname_np() doesn't have the "thread" argument on OS X.

For debugging.

The update thread should not affect the rest of the system, therefore
set "idle" priority, and let it only run when nobody else is using the
resources.

Allows forward-declaration.

Remove a GLib dependencies from class EventLoop and DatabaseLock.

Use CRITICAL_SECTION and CONDITION_VARIABLE.  This requires Windows
Vista or newer.  It fixes problems with GLib threading objects that
were implicitly created by static constructors before g_thread_init().

Switch WIN32 to this implementation to be able to use condition
variables, which is impossible with CriticalSection.

Use a custom pthread_mutex_t wrapper because std::mutex adds overhead.