Remove the runtime check for eventfd(), hard-code the feature once
it's been selected at compile time.  The class WakeFD is splitted into
EventFD and EventPipe, using WakeFD as a macro diversion.

Don't deinterleave manually, don't allocate memory.

Simplify the error path, because the other allocations may fail.

Player_LoadTitle() returns an aligned pointer in libmikmod-3.2 that
cannot be freed with free(). The correct way to do this now is
MikMod_free() which extracts the original pointer from the buffer and
frees that.
Signed-off-by: Christoph Mende <mende.christoph@gmail.com>

Fixes Mantis #3770.

Fix for Mantis #3806.

"PcmBuffer::Clear clears the buffer but does not reset the size. If
Get is called on the same PcmBuffer later on with a size that is the
same as (or less than) it was before the call to Clear, the "else"
branch is taken and the memory of buffer (at the address of nullptr)
is poisoned instead of the necessary allocation being performed. A
memset or memcpy on the returned pointer (nullptr) causes a
segmentation fault."