The sequence

  #define m()
  int m"

creates a token of no length (a string of 0 size).  Protect
against a string of 0 size as well as the existing protect
against a null string.

This would look ahead for a second #, for token pasting, and if not
found, backup one token.  This is fine, unless at the end of line,
which would backup the #, rather than the look ahead.

HLSL: allow trailing commas in initializer lists & scalar initialization

HLSL: Fix a grammar error related to constructors in paren expr

Single member structs initialized with an initializer list had
an incorrect argument for constructor emulation.

SPV: Fix an issue of ++/-- for dvec/dmat.

Also, this allows turning on the error check for a failed assigment
when parsing.

This makes 39 HLSL tests have a working assignment that was previously
silently dropped, due to lack of this functionality.

HLSL: add Buffer support for Load method

HLSL: add missing vec,vec,scalar form of lerp(), + test

HLSL: allow uint literals, and add test for numeric suffixes

HLSL: Add CalculateLevelOfDetail, and unimplemented errors for *Uncla…

Missing are implicit conversions between int/bool/etc.

Starting out with this turned off, so tests can be locally fixed,
then will turn it on.

HLSL: add 2DMS texture formats, and matching Load / GetDimensions sup…

Apply the interpolation first, then apply the swizzle to the result,
the inverse of the order requested by the AST.  This fixes issue #411.

HLSL: Add gather, improve proto generator machine for upcoming 2DMS/S…

HLSL: enable #line extension by default for HLSL source.

Remapper: Remap Scope and MemorySemantics IDs in SPIRV remapper

Scope and MemorySemantics operands contain IDs as well and may need
remapping.