The particular need on this is because of the current situation
with determining the background functionality for the
gettimeofday. DllMain allows to initialize stuff before the DLL
can be actually used. Thus, we use different time API on win7
and win8 and later, so the function pointer needs to be
initialized before anything in the DLL could even demand it.
The change also opens the door for the further optimizations,
as now we're able to do the very basic initializations for the
whole DLL before it could ever start to live. Fe on this way the
TLS initialization could be done, when utilizing the
DLL_THREAD_ATTACH/DETACH case. Whether it's really usable in
portable way should be synced with other platforms.
Be aware that it's dangerous as it possibly causes dead locks.
So to use with care. One willing to add items to DllMain should
better read the documentation twice and even then try to defer
the necessary action.