osx: implement DarwinSemaphore.cpp

OSX pthreads doesn't implement sem_timedwait(), which is a real shame. The
Mach subsystem does have a semaphore_timedwait() variant though.

This code is untested, and server mostly as a reference and to test and
improve the final implementation once OSX/64-bit can properly compile.
osx: define _CVTBUFSIZE for POSIX, not just Linux
osx: don't build MemcpyFast.S

It doesn't properly build on OSX (binutils...) and it wasn't being used any
way (OSX has a fast memcpy and memcmp).
osx/clang: use the integrated assembler on osx

It seems to work fine, and provokes less warnings while linking. The real
reason for this commit is issue #303 though. No xgetbv = no fun (and by fun
I mean AVX).
64-bit: get rid of 64-bit warnings in emitter

Doesn't really functionally change a lot, but if we ever want to get this
working on 64-bit... baby steps.
osx: use POSIX AIO, not Linux kernel AIO

Also enables building of pcsx2 core, which fails horribly of course.

- OSX doesn't have the concept of librt as a separate piece of its Libc. So
  we don't check for that

Credit goes to @juhalaukkanen

reference for Linux AIO and POSIX AIO:
https://code.google.com/p/kernel/wiki/AIOUserGuide
http://www.fsl.cs.sunysb.edu/~vass/linux-aio.txt
64-bit,UNIX: stdcall/callback doesn't exist

As far as I could find. On 64-bits/OSX at the very least the compiler
signals that it just doesn't exist. The calling conventions were unified for
all 64-bit UNICES. So this fix should also be good for 64-bit Linux.
osx: implement DarwinMisc.cpp

Accurate low-overhead timing and memory stats.