scheduler: Make HaveReadyThreads() a const member function

Fixed a bunch of race conditions when running in multicore mode.

Kernel/Mutex: Don't duplicate threads in the mutex waiter list.

gl_shader_decompiler: Implement XMAD instruction.

Another thread may write to this variable while the core in question is in the middle of checking for a reschedule request.

Another thread might be in the middle of an SVC, thus altering the state of the schedulers.

Another thread might be in the middle of a reschedule, thus altering the state of the schedulers.

WakeAfterDelay might be called from any host thread, so err on the side of caution and use the thread-safe CoreTiming::ScheduleEventThreadsafe.

Note that CoreTiming is still far from thread-safe, there may be more things we have to work on for it to be up to par with what we want.

vfs: Make type hierarchy objects classes instead of structs

Exit from AddMutexWaiter early if the thread is already waiting for a mutex owned by the owner thread.

This accounts for the possibility of a thread that is waiting on a condition variable being awakened twice in a row.

Also added more validation asserts.

This should fix one of the random crashes in Breath Of The Wild.

Makes it consistent with the other VFS interfaces and prevents implicit
construction.

struct should be used when the data type is very simple or otherwise has
no invariants associated with it. Given these are used to form a
hierarchy, class should be used instead.

Fixed invalid cast in loader

cubeb_sink: Protect queue with a mutex

GetAudioDeviceServiceWithRevisionInfo (Used by Bloodstained: Curse of the Moon)

Added GetAudioRendererSampleRate, GetAudioRendererSampleCount & GetAudioRendererMixBufferCount

 hid: Stub DisconnectNpad() 

externals: Update to SDL2-2.0.8.

GL renderer: Pick the streambuffer from citra and use them.

This function doesn't modify instance state, so the const qualifier can
be added to it.

These don't directly modify the contained data.

Don't emut copies, especially not for data, which is used once. They just end in a huge GPU overhead.

Please see https://github.com/citra-emu/citra/pull/3666 for more details.

As we're not handling any anything about the revision data for GetAudioDeviceServiceWithRevisionInfo, it's currently marked as stubbed. However for games this shouldn't affect the result. Proper revision info would be more for homebrew.

Prevents clang-format from butchering them.

This is required by ARMS.

gl_shader_decompiler: Fix SetOutputAttributeToRegister empty check.

 CMakeLists: Change MSVC14 variable to MSVC_VERSION

GetAudioRendererSampleRate is set as a "STUB" as a game could check if the sample rate it sent and the sample rate it wants don't match. Just a thought of something which could happen so keeping it as stub for the mean time