HLSL: Translate directive [flatten] and [branch] to SPV control mask.

Implement SPV_KHR_post_depth_coverage

Added support for both extension GL_ARB_post_depth_coverage and GL_EXT_post_depth_coverage.

HLSL: handle type conversion for any/all intrinsics

HLSL allows float/etc types for any/all intrinsics, while the
SPIR-V opcode requires bool.  This adds a simple decomposition
to type convert the argument.  It could get a little more clever
in some of the type cases if it ever had to.

Add option to skip installation

Fix CMake scripts to set the POSITION_INDEPENDENT_CODE property correctly

Fix CMake scripts: The set_property script can be used to set only a single property, so now setting the POSITION_INDEPENDENT_CODE property correctly.

As a static target, when included in other cmake projects, it is not needed to install these libraries and headers as part of this build, and just need to link to this.

Multiview extension: Accept layout(num_views) qualifier

Lays the groundwork for fixing issue #954.

Partial flattenings were previously tracked through a stack of active subsets
in the parse context, but full functionality needs AST nodes to represent
this across time, removing the need for parsecontext tracking.

This commit, and next one, are specifically to make a future commit
handling partial dereferences of flattening objects easier to see.

io resolver improvements

Fix for not transforming all image symbols into sampled images symbols

- adds stage parameter to end notify
- adds begin notify
- adds begin resolve
- adds end resolve

Change-Id: Ib134fe42a1a6d996d81dca59475cce6b4a9ff865

Implement extensions GL_OVR_multiview and GL_OVR_multiview2

They are almost identical to the already supported GL_EXT_multiview

Change-Id: I10f9bcea2e97f36912a81214552b93db4805b61a

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