HLSL: force textures to shadow modes from combined samplers

Texture shadow mode must match the state of the sampler they are
combined with.  This change does that, both for the AST and the
symbol table.  Note that the texture cannot easily be *created*
the right way, because this may not be known at that time.  Instead,
the texture is subsequently patched.

This cannot work if a single texture is used with both a shadow and
non-shadow sampler, so that case is detected and generates an error.
This is permitted by the HLSL language, however.  See #1073 discussion.

Fixed one test source that was using a texture with both shadow and
non-shadow samplers.

Legalization: Fix warnings and disable tests when spirv-tools not present

Enable HLSL legalization

Also added known-good mechanism to fetch latest validated spirv-tools.
Also added -Od and -Os to disable optimizer and optimize for size.

Fetching spirv-tools is optional for both glsl and hlsl. Legalization
of hlsl is done by default if spirv-opt is present at cmake time.
Optimization for glsl is currently done through the option -Os.

Legalization testing is currently only done on four existing shaders.
A separate baseLegalResults directory holds those results. All previous
testing is done with the optimizer disabled.

Implement extension GL_NV_shader_atomic_int64

Travis: use make instead of ninja

Remapper: make remapper robust against non-exiting error handlers

CMake file changes for SPIR-V legalization for HLSL

Cmake now looks for External/spirv-tools. If found, it links in
SPIRV-Tools-opt and SPVRemapper, and adds -DENABLE_OPT to build.

Remapper errors are generally fatal: there has been some unexpected situation while
parsing the SPV binary, and there is no reasonable way to carry on.  The
errorHandler() function is called in this case, which by default exits, but
it is possible to submit a handler which does not.  In that case the remapper would
carry on in a bad state.

This change ensures a graceful termination of the remap() function.

While a try {} catch {} construct would be the ideal and safe way to do this,
that's off limits for certain environments, so this tries to do the same thing
with explicit code, to catch all the bailout paths.

Add support for GL_OES_EGL_image_external_essl3

HLSL: allow split type in InputPatch template type, & HS return types.

InputPatch parameters to patch constant functions were not using the
internal (temporary) variable type.  That could cause validation errors
if the input patch had a mixture of builtins and user qualified members.

This uses the entry point's internal form.

There is currently a limitation: if an InputPatch is used in a PCF,
it must also have appeared in the main entry point's parameter list.
That is not a limitation of HLSL.  Currently that situation is detected
and an "implemented" error results.  The limitation can be addressed,
but isn't yet in the current form of the PR.

Hull shaders have an implicitly arrayed output.  This is handled by creating an arrayed form of the
provided output type, and writing to the element of it indexed by InvocationID.

The implicit indirection into that array was causing some troubles when copying to a split
structure.  handleAssign was able to handle simple symbol lvalues, but not an lvalue composed
of an indirection into an array.

There was some ambiguity/contradiction in this behavior, and
Khronos decided glslang should always have these outside blocks,
rather than have stage/vendor/target variations.

GLSL: Promote HLSL entry-point renaming code to be used by GLSL as well.

Fixes #1045.

Implement the extension GL_AMD_shader_fragment_mask

Build: Fix strdup -> _strdup warnings.

Delete unused 'this' capture

Remove an unused 'this' entry from a lambda capture list.

This cleans up a unused-lambda-capture warning.