externals: Update to SDL2-2.0.8.

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

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.

gl_shader_decompiler: Fix SetOutputAttributeToRegister empty check.

 CMakeLists: Change MSVC14 variable to MSVC_VERSION

Stub UpdateUserPresence

gl_shader_decompiler: Fix GLSL compiler error with KIL instruction.

Needed for Retro City Rampage to go in game

Several Friend service fixes

core: Namespace EmuWindow

gl_rasterizer: Silence implicit truncation warning in SetupShaders()

GPU/Maxwell3D: Implemented an alternative set of blend factors.

RasterizerGL: Ignore invalid/unset vertex attributes.

These are used by nouveau and some games like SMO.

- Used by Go Vacation

This should make the es2gears example not crash anymore.

- Used by Splatoon 2.

Previously this would warn of truncating a std::size_t to a u32. This is
safe because we'll obviously never have more than UINT32_MAX amount of
uniform buffers.

Gets the class out of the global namespace.

gl_shader_decompiler: Improve handling of unknown input/output attributes.

Implement render target formats RGBA8_SNORM and RG8_SNORM.

The rest of the CMake script uses lowercase for commands (which is the
general CMake style), making it more consistent with surrounding code.

Use of the MSVC14 variable is discouraged in the CMake documentation
(which makes sense, since MSVC_VERSION is the more general appliable
variable).

loader: Add more descriptive errors

GPU/Shader: Implemented SSY and SYNC as a set_target/jump pair.

- Used by Super Mario Odyssey.

- Used by Super Mario Odyssey.

SSY sets the target label to jump to when the SYNC instruction is executed.