When capabilities are needed for specific SPIR-V instructions, it is
fragile to do so based on GLSL/AST usage; it should be based on actual
instructions they got translated to.

Tests: Add more string -> float tests. Related to #1456.

Possibly addresses #1456

Fixes a crash when in/out varying variable had no semantic name and a…

 Match https://github.com/KhronosGroup/GLSL/pull/22

Fixes a crash when in/out varying variable had no semantic name and an error was reported in ioremapper phase when the variable was rejected

GLSL/SPV: If a texture is used with a shadow sampler, force 'shadow'.

Update spirv-tools known good

Tracks https://github.com/KhronosGroup/GLSL/pull/22.

Fixes #854. But, only good if we are not trying to use the same
texture for both shadow and non-shadow constructors.

Force the type of the texture to have 'shadow' set when it is
constructed with a samplerShadow.

Includes the following:

Add Vulkan 1.1 capability sets
Don't merge types of resources
Remove stores of undef.
Make sure the constant folder get the correct type.

Link: Merge all downstream consumed intermediate modes.

Fixes #1309.

build: Add ccache option to CMake config

Link/SPV: Correct symbol IDs on merging ASTs to a single coherent space

CMake options for postfix and SPVRemapper.

Merge branch 'missing_descriptor_indexing_extension' of https://github.com/jeffbolznv/glslang into jeffbolznv-missing_descriptor_indexing_extension

This is one step in providing full linker functionality for creating
correct SPIR-V from multiple compilation units for the same stage.
(This was the only remaining "hard" part. The rest should be simple.)

NDK build: Use NDK r17b and its own CMake toolchain file

More recent NDK releases have their own CMake toolchain file.
Use it.

Also, download the NDK from github.com:dneto0/android-ndk.
That is a fork of the repo we used to use, but we have more
control over how long it stays stable.

WIP: Travis-CI: Use Android NDK r13b specifically   

The Travis-CI bot downloads a copy of the Android NDK.  The source
we get it from recently updated to Android NDK r17b.  However,
the android.toolchain.cmake file does not know how to parse the
Android native API level from that version of the NDK.  So check
out the NDK r13b version that we were using until yesterday.

Fixes #1439

Reflection exposes the Shader Stages where a Uniform is present

Use public SPIRV-Tools header

This is totally optional, but lets people build this repo with
ccache to improve rebuild speeds.  It also can help a great deal
on ccache-enabled CI systems like Travis-CI.  We build fixed
revisions of glslang a lot on Travis, so this will be a big help
with CI machine loading.