This script will crank a supplied set of glslang test shaders through the
spirv-val tool, reporting on the results.

There are some important things to note:

* Like 'runtests', this must be invoked from the 'Test' subdirectory.

* This is mostly useful on the hlsl.* tests, although it is not strictly
limited to those.  The reason is that most of the glsl tests either contain
validation error cases, and so fail to compile, or are not using a #version
compatible with producing SPIR-V modules.

* Some tests, such as negative tests, or most of the glsl tests, have
intentional compilation errors.  This script treats that as OK.  Failures
are successfully compiling shaders which proceed to fail spirv-val.

* spirv-val is looked for in either the External directory, or if not
found there, in a sibling directory of glslang, and if not found there
either, in /usr/local/bin.

* There are a bunch of command line options.  ./validate-shaders.sh --help
will describe them.

Some examples to try:

   ./validate-shaders.sh hlsl.*   # exercise all hlsl.* tests.
   ./validate-shaders.sh --terse hlsl.*  # same, but tersely.

   # dump validator results for problems in something.frag:
   ./validate-shaders.sh --quiet --dump-val something.frag

Remapper: Fix strip algo when strip ranges overlap

To handle sparse assignments, don't check maxCombinedTextureImageUnits.

Add python3 compatibility to update_glslang_sources.py

Both debug and release clang builds have segfaulted on recent
changes, non deterministically, while doing the single/multi-thread
test all test files. Removing recent test files, to see if it gives
a clue.

GLSL: Fold constant SHRT_MIN/INT_MIN/LLONG_MIN % -1 to 0.

GLSL: Check for implicit inner dimension in array of atomic_uint.

Preprocessor: Evaluate INT_MIN % -1 to 0.

Update spirv-tools known-good

Only try swizzles on vectors, numbers, and booleans.

Merge branch 'only-parse-inf-constant-in-hlsl' of https://github.com/xorgy/glslang into xorgy-only-parse-inf-constant-in-hlsl

Check for hexadecimal literals exceeding MaxTokenLength.

Nonfunctional: minor: use std::array for per-set shifts, fix warning.

Two unrelated, minor tweaks:

(1) Use std::array for shiftBindingForSet.  Now matches shiftBinding.
(2) Add parens in shouldFlatten() to make compiler warning happy.

Add per-descriptor-set IO mapping shift values.

This PR adds the ability to provide per-descriptor-set IO mapping shift
values.  If a particular binding does not land into a per-set value,
then it falls back to the prior behavior (global shifts per resource class).

Because there were already 6 copies of many different methods and internal
variables and functions, and this PR would have added 6 more, a new API is
introduced to cut down on replication and present a cleaner interface.
For the global (non-set-specific) API, the old entry points still exist
for backward compatibility, but are phrased internally in terms of the
following.

    // Resource type for IO resolver
    enum TResourceType {
        EResSampler,
        EResTexture,
        EResImage,
        EResUbo,
        EResSsbo,
        EResUav,
        EResCount
    };

Methods on TShader:

    void setShiftBinding(TResourceType res, unsigned int base);
    void setShiftBindingForSet(TResourceType res, unsigned int set, unsigned int base);

The first method replaces the 6 prior entry points of various spellings, which
exist now in depreciated form.  The second provides per-resource-set functionality.
Both accept an enum from the list above.

From the command line, the existing options can accept either a single shift value as
before, or a series of 1 or more [set offset] pairs.  Both can be provided, as in:

    ... --stb 20 --stb 2 25 3 30 ...

which will use the offset 20 for anything except descriptor set 2 (which uses 25) and
3 (which uses 30).

Desktop defaults to highp for samplers, but this should not apply to the built-in
functions, so make it appy only to user declarations.

Preprocessor: Evaluate INT_MIN / -1 to 0.