video_core: Remove a few unused variables and functions

CMakeLists: Specify /volatile:iso for MSVC

CMakeLists: Explicitly specify -Wall for the non-MSVC case

Rasterizer Cache: refactor flushing & optimize memory usage of surfaces

Silences a -Wreorder warning.

This isn't used at all, so it can be removed.

This variable is unused entirely, so it can be removed.

Instead of retrieving the data from the std::variant instance, we can
just check if the variant contains that type of data.

This is essentially the same behavior, only it returns a bool indicating
whether or not the type in the variant is currently active, instead of
actually retrieving the data.

Silences a few compilation warnings.

By default, MSVC doesn't use standards-compliant volatile semantics.
This makes it behave in a standards-compliant manner, making
expectations more uniform across compilers.

service/audctl: Update documentation comments to be relative to 8.0.0

src/CMakeLists: Add /Zc:externConstexpr to the MSVC build flags

Fix Layered ASTC Textures

gl_shader_disk_cache: Skip stored shader variants instead of asserting

Port citra-emu/citra#4749: "web_service: Misc fixes"

yuzu/hotkeys: Remove unnecessary constructor

yuzu/compatdb: Remove unnecessary qualifiers

configure_dialog: Remove the Whats This? button from the dialog

core/memory: Remove unused FlushMode enum

Corrections and Implementation on GPU Engines

externals: Update dynarmic to master

The behavior of the Hotkey constructor is already accomplished via in-class member
initializers, so the constructor is superfluous here.

Keeps the code consistent in regards to how the buttons are referred to.

The C++ standard allows constexpr variables declared with the extern
keyword to have external linkage. Previously MSVC wasn't abiding by
this. This just makes the compiler more standards compliant during
builds.

Given we currently don't make use of anything that would break by this,
this is safe to enable.

Makes it much nicer to visually scan the options. This also starts the
flag descriptions from the same column for the same reason.

Recent changes to memory-related code resulted in this being unused, so
we can remove it.

Better instruction support has been added since the last update.

travis: Update to using Xcode 10.2

Keeps the CI toolchain updated. This is also necessary for updating
dynarmic.

core/frontend/emu_window: Make GraphicsContext's destructor virtual

common/zstd_compression: Remove #pragma once directive from source file

gl_rasterizer: Silence unused variable warnings

The backend is not used until we decide to submit the testcase/telemetry, and creating it early prevents users from updating the credentials properly while the games are running.

This isn't used anywhere, so we can get rid of it.

Ensures that -Wall is always active as a compilation flag.

Makes use of src, so it's not considered unused.

Introduced in 72477731. This is only
necessary within header files.