Add CMake build system files (incomplete)

This ports most of configure to CMake. Some parts (like CoreAudio
and Apple Remote on OS X) are still missing.

Probably breaks stuff left and right due to lack of testing.

cmake/mpv/Utils: Fix static linking option

CMake: Fix dsound option

CMake: Fix timer-win2.c typo

CMake: Add MinGW-specific definitions

CMake: Fix socket lib checks on Win32

CMake: PortAudio wants pthreads

CMake: Fix static linking of libquvi

CMake: Fix static linking of libbluray

CMake: Add missing lib on Win32

CMake: Fail with more descriptive error on unset CPU arch

CMake: Fix FindOSS

Also use a preprocessor macro to store the path to soundcard.h

timer-linux: Remove use of obsolete usleep

CMake: lower minimum required version to 2.8
Add CMake cross-compilation howto