This CL allows setting the location of glslangValidator and spirv-remap
when calling the runtests script. A test target is added to CMake to
execute runtests and sets the location to the build folder for the two
applications.

Export glslang targets on installation

find Python and add External subdir only if BUILD_EXTERNAL option was set

find Python and add External subdir only if BUILD_EXTERNAL option was set (on by default) and /External dir exists

Add support for GL_ARB_explicit_uniform_location

Fixed typo in README.md

Remove unnecessary semi-colons and add warning about them

These are causing integration issues with Chromium down stream since
it is more strict about these.

Adjusting code interface

Update spirv-tools known good.

If the semantics that require the KHR form over the EXT form are seen
(OpBitcast between a vector and a pointer) promote the requested extension
from the EXT to the KHR.

The KHR form comes along as part of 1.5, and otherwise should require
another form of request to emit it.

Move install directory for SPIRV/ folder.

Currently the SPIRV/ folder will get installed into the include
directory. This folder is part of GLSLang, so it makes more sense under
glslang/SPIRV.

Currently, GLSLang will install a SPIRV/ folder while spirv-headers will
install a spirv/ folder. This is confusing and will cause issues on a
case sensitive filesystem if both are installed at the same time.

HLSL: Add attributes for image formats and nonreadable/nonwritable

Reflection will crash when the VS input symbol defines the same name with FS output symbol

GLSL/SPV: Fix #1900: Drop const on literal when doing an object copy.

Separate GLSLANG_WEB (min-size build) and Emscripten options

SPV_KHR_physical_storage_buffer/SPV: Add GL_EXT_buffer_reference_uvec2

Adds uvec2 <-> reference constructor support.
Switches from EXT to KHR for physical_storage_buffer.

Fix Fuchsia build.

The Fuchsia build is very picky about newlines at the end of files
and will complain loudly about them. Removing the -Wnewline-eof
warning solves the issue.

Allows building non-min-size builds with Emscripten.
Adds ENABLE_GLSLANG_WEB_DEVEL.
Moves the glslang.js files to OSDependent/Web.
Small cleanups and docs update.