The memory model group agreed to these definitions for how
to map GLSL barrier, memoryBarrier, etc. With HLSL following suit.

Update spirv-tools known-good.

Fixes #1188.

SPV: Implement XFB

Also, only emit this XFB information where the SPIR-V spec says
it should be emitted: essentially, on objects.

This and the previous commit together fix #1185.

Add implementation of SPV_EXT_fragment_fully_covered

This implementation uses the GLSL extension
GL_NV_conservative_raster_underestimation to generate the new SPIR-V
FullyCoveredEXT built in.

HLSL: for split output structs, propagate indirection to builtins.

HLSL: Implement support for RT/Viewport output from VS

In DX10/DX11 you can only output RT/Viewport indices from GS; however,
DX11.4/DX12 add support for outputting these from VS as well.

This is supported by Vulkan if the relevant extension is available, and
by MSL and by MSL (which you can cross-compile to via SPIRV-Cross).

Some stage (e.g, hull shaders) have arrayed builtin outputs (e.g, position).
When copying from the internal structure to the split form, it is necessary
to propagate that indirection to the actual arrayed outputs.  This was not
happening.

Addresses #1181

HLSL: add optional position.Y inversion

This was listed as outputs for tessellation stages, but they
are input only.

HLSL: Allow primitive id on hull shader input

HLSL: Stop flattening non-IO structs containing opaques.

Fixes #979

This makes struct returns from functions work, but breaks
structs containing arrays, due to limitations in subsequent
transforms in spirv-opt. This is expected to be fixed soon.

Adds command line options:

   --invert-y
   --iy

(synonyms) which invert position.Y on vertex shader output.  Handles these cases:

* Direct single variable return
* Member of direct returned struct
* Single variable output parameter
* Member of struct output parameter

API:

    // Enables position.Y output negation in vertex shader
    void TShader::setInvertY(bool invert);

Fixes #1173

Improve build instructions

- Mention that the instructions are written for Bash.
- Quote the CMAKE_INSTALL_PREFIX to handle spaces in $(pwd).
- Remove SSH clone instructions. Instructions on how to clone are for
  those unfamiliar with GitHub, so fewer options are better and SSH
  requires additional configuration to make work.
- Replace ninja with make, because more people are familiar with it and
  we probably don't need to explain how to install it. Fixes #956.
- Remove the section mentioning cygwin, as it's unclear and doesn't
  seem necessary.
- Mention minimum language version in the Dependencies section.
- Move `cd $BUILD_DIR` out of the Linux configuration section because
  it's needed on both platforms. Add a line about creating the build
  directory, too.

This continues to prevent writing output buffers (out from a function),
but fixes the problem where the copy-in/out was not getting done.

Making everything work will require knowing both in/out-ness and bufferness,
but these are currently mutually exclusive, because both are storage
qualifiers.

Update spirv-tools known-good

HLSL: minor: add warning for mat() matrix size truncation

This fixes spirv-tools issue 989 where if-break can be incorrectly
deleted from a loop.

Minor change to add a compilation warning on implicit matrix size
truncations.

(This is motivated by wanting to retickle the tests.)

#1165 invalid store