Implement extensions GL_OVR_multiview and GL_OVR_multiview2

They are almost identical to the already supported GL_EXT_multiview

Implement extension GL_ARB_shader_stencil_export

Fixing initialization order to fix -Wreorder warning in clang.

Some layout qualifiers must not be on an object and had a TBD for testing
them: early_fragment_tests, cw/ccw, points, point_mode, and
fractional_even_spacing/fractional_odd_spacing/equal_spacing.

Add support for GL_EXT_shadow_samplers

Compilation-environment control

This is for input languages, client APIs, code to generate, etc.

HLSL: handle clip/cull distance array semantic matching

In HLSL, there are three (TODO: ??) dimensions of clip and cull
distance values:

  * The semantic's value N, ala SV_ClipDistanceN.
  * The array demension, if the value is an array.
  * The vector element, if the value is a vector or array of vectors.

In SPIR-V, clip and cull distance are arrays of scalar floats, always.

This PR currently ignores the semantic N axis, and handles the other
two axes by sequentially copying each vector element of each array member
into sequential floats in the output array.

Fixes: #946

hlsl: "in out" is also an inout qualifier.

Addresses #940.

Top of master is listing a test error, not from glslang, but internally
within Travis itself.  Seeing if another run gets it to work again.

Replace #422: Remove the redundant location setting in AST->SPIR-V.

Works for both GLSL and HLSL.
Fixes #87.

ShaderCompUnit was poorly done, a mix of a list of things and hard
coding to a single thing. This makes it all a true list.

File data was greatly simplified to be a single string, no longer
supporting breaking a single file into multiple strings.

Makes alphabetical order, fit in 80 columns, abstract in-option
string argument.

HLSL: fix several issues in mat construction from scalars

This fixes:

1. A compilation error when assigning scalars to matricies

2. A semantic error in matrix construction from scalars.  This was
initializing the diagonal, where HLSL semantics require the scalar be
replicated to every matrix element.

3. Functions accepting mats can be called with scalars, which will
be shape-converted to the matrix type.  This was previously failing
to match the function signature.

NOTE: this does not yet handle complex scalars (a function call,
say) used to construct matricies.  That'll be added when the
node replicator service is available.  For now, there's an assert.

There's one new test (hlsl.scalar2matrix.frag).  An existing test
lsl.type.half.frag changes, because of (2) above, and a negative
test error message changes due to (3) above.

Fixes #923.

SPV: Fix an typo of SPV_AMD_texture_gather_bias_lod

E.g., in

    float float;
    (float) * float;

The "(float)" is not a type cast, it is an expression.