HLSL: Fix possibly incorrect type conversion in Store2-3-4

This is to create more stable test results.

This allow for propagation through structs with dynamically indexed
arrays. This supports recent removal of non-io struct flattening.

Set type to r-value resulting from indexing vector, to prevent
float->uint conversion when source is already uint. Resulting
OpConvertFToU would otherwise fail validation because source is
already uint.
For LoadN, incorrect uint->float->uint can be avoided; fixing
potential truncation of big integer values.

compile error fix for g++ 5.4.0

Fix compilation error under g++ 5.4.0.

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