HLSL: Fix #1249: Always execute both sides of ternary "?:".

This is semantically required by HLSL, and frequently results in using
OpSelect instead of control flow.

HLSL: Add conversions for image ops during SPV construction

HLSL allows image and texture types to be templatized on sub-vec4 types,
or even structures.  This was mostly handled already during creation of
sampling operations.  However, for operator[] which can generate image
loads, this wasn't happening.

It also isn't very easy to do at that point in time, because operator[]
does not know where the results it produces will end up.  They may be
an lvalue or an rvalue, and there's a post-process to convert loads to
stores.  They may end up in atomic ops.

To bypass that difficulty, GlslangToSpv now looks for this case and
adds the appropriate conversion.  LIMITATION: this only works for
cases for which a simple conversion opcode suffices.  That is to say,
it will not work if the type is templatized on a struct.

Fix an issue of interpolateAtVertexAMD().

An error message should be reported if the interpolant is not an input.

Update SPIRV-Tools known-good

Upgrade update_glslang_sources.py to work with other sites

One legalization case updated for a renumbered ID

--site gitlab must be added to command for gitlab capability.
Default is github.

Add DeadInsertElim to legalization and RedundancyElim to -Os.

SPV: Create more access chains addressing a few swizzling issues.

Preprocessor: Use std::string instead of std::stringstream

- Fixes #1233
- Treats local bools like anything else
- more consistently deals with a dynamic component selection

std::stringstream has a measurable overhead for preprocessing - it
appears that operator<< does a tiny bit of extra work for appending
chars/strings and also can't be inlined in most cases on VS2015;
additionally, std::endl triggers a stream flush which also adds up.

Replacing this with std::string buffer gets the preprocessing time down
from 180ms to 135ms in one case, making it 1.33x faster.

Note that integer-to-string conversion is using std::to_string; in
theory this could be slower than sprintf or manual conversion, but I
haven't found these cases to affect preprocessing time in practice
(std::to_string would always use the short string buffer for
line/version numbers, and the number of calls is not too significant).

Update SPIRV-Tools known-good

Update SPIRV-Tools.  Relevant functional changes:
 - Optimizer enhancements:
   - ADCE now removes OpSwitch
   - Block merging occurs in more cases
 - Optimizer fixes:
   - Constant propagation (CCP): support matrix constants
   - #1199: Optimizer: Fix CCP: don't propagate spec constants.
   - #1203: Optimizer: Fix common uniform elim bug introduced by refactoring.
   - #1210: Optimizer: Aggressive dead code elimination: Fix 'break' identification.
   - #1212: Optimizer: Aggressive dead code elimination: Was skipping too many instructions.
   - #1214: Optimizer: Aggressive dead code elimination: Fix infinite loop.
   - #1228: Optimizer: Fix CCP: Handling of varying Phi nodes; was resulting in infinite loop.
   - #1245: Optimizer: Dead branch elimination: Avoid a null pointer dereference.
   - #1250: Optimizer: Dead branch elimination: Avoid spuriously reporting a change.
   - #1262: Support building on VisualStudio 2013 again

Update SPIRV-Headers, with "unified1" directory.

Updated one Glslang legalization test base result due to better block merging.

Control flow attributes

See https://github.com/KhronosGroup/GLSL/pull/11.

- make it sharable with GLSL
- correct the case insensitivity
- remove the map; queries are not needed, all entries need processing
- make it easier to build bottom up (will help GLSL parsing)
- support semantic checking and reporting
- allow front-end dependent semantics and attribute name mapping

Fixes #1236.

Fix unused function warning.

Update known-good spirv-tools.

TGlslangToSpvTraverser::getExtBuiltins is only used when AMD_EXTENSIONS
is defined, so only define it in that case to avoid an unused function
warning.

Optimizations used in HLSL legalization now sweep away unused types.