HLSL: implement [unroll] and [loop] attributes

This adds infrastructure suitable for any front end to create SPIR-V loop
control flags.  The only current front end doing so is HLSL.

[unroll] turns into spv::LoopControlUnrollMask
[loop] turns into spv::LoopControlDontUnrollMask
no specification means spv::LoopControlMaskNone

Fix iomapper build warnings

HLSL: Implement missing GatherCmp method

Modernise CMake #2

This reverts commit cfc69d95.
* Change CMAKE_INSTALL_PREFIX default on Windows in order
  to prevent permission denied errors when trying to install
  to "Program Files".

Revert "Modernise CMake"

Modernise CMake

* Use `GNUInstallDirs` in order to respect GNU conventions.
  This is especially important for multi-arch/multi-lib setups.
* Specify position independent mode building properly, without
  using the historic hack of adding `-fPIC` as a definition.
  This makes the build system more portable.
* Only detect C++ (and not C) to slightly speed up configuring.
* Specify C++11 mode using modern CMake idioms.
* Fix some whitespace issues.

Notification phase for io remapper

HLSL: Allow empty struct initializers

Adds a notification phase to the io remapper.
The idea behind this is to give the user a
chance to group uniforms and/or in/out variables
for a better pipeline layout sharing for vulkan.

Change-Id: I7492421085a4156ed3534f01d906ab390d73a623

Review request: does this harm GLSL in any way?

HLSL: add standard sample position return form of GetSamplePosition m…

Multisample textures support a GetSamplePosition() method intended to query
positions given a sample index.  This cannot be truly implemented in SPIR-V,
but #753 requested returning standard positions for the 1..16 cases, which
this PR adds.  Anything besides that returns (0,0).  If the standard positions
are not used, this will be wrong.

This should be revisited when there is a real query available.

HLSL: Add ConstantBuffer<T> syntax

Note: multi-dimension arrays of ConstantBuffer objects will go through uniform flattening.

Fix Android build errors

glslang/MachineIndependent/iomapper.cpp:207:9: error: field 'resolver' will be initialized after field 'stage' [-Werror,-Wreorder]
      : resolver(r)
        ^
glslang/MachineIndependent/iomapper.cpp:263:9: error: field 'resolver' will be initialized after field 'stage' [-Werror,-Wreorder]
      : resolver(r)
        ^
hlsl/hlslParseHelper.cpp:70:5: error: field 'gsStreamOutput' will be initialized after field 'inputPatch' [-Werror,-Wreorder]
    gsStreamOutput(nullptr),
    ^

HLSL: add error for expected comparison sampler in SampleCmp* ops

This adds an error message if a non-comparison sampler is used with
comparison sampling methods.  There's no functional change for correct shaders.

Vector conditions properly convert the true/false expression types to same
width vector as the condition.

Scalar conditions make the true/false expressions convert to each other.

HLSL: fix for byte address buffers in fn parmeters

HLSL: cast non-int types to uint on Load/Store indexes

HLSL: hlsl register class iomapping

Byte address buffers were failing to detect that they were byte address
buffers when used as fn parameters.

Note: this detection is a little awkward, and could be simplified if
it was easy to obtain the declared builtin type for an object.

Adds --hlsl-iomap option to perform IO mapping in HLSL register space.

--shift-cbuffer-binding is now a synonym for --shift-ubo-binding.

The idea way to do this seems to be passing in a dedicated IO resolver, but
that would require more intrusive restructuring, so maybe best for its
own PR.

The TDefaultHlslIoResolver class and the former TDefaultIoResolver class
share quite a bit of mechanism in a common base class.

TODO: tbuffers are landing in the wrong register class, which needs some
investigation.  They're either wrong upstream, or the detection in the
resolver is wrong.

Also, fixed one test file that didn't have its syntax error as the last line.

Some texture and SB operations can take non-integer indexes, which should be
cast to integers before use if they are not already.  This adds makeIntegerIndex()
for the purpose.  Int types are left alone.

(This was done before for operator[], but needs to apply to some other things
too, hence its extraction into common function now)

Longer term, this storage class should be generated based on the mode
of compilation.

HLSL: structuredbuffer counter functionality