Add Bazel build files and bots for them

Only apply volatile semantics to atomics when using Vulkan Memory Model

In order to avoid potential build failures that could arise from
SPIRV-Tools/Headers, and to avoid reading known_good.json, this build
configuration does not build the SPIRV-Tools dependency and hence cannot
perform HLSL compilation to SPIR-V.

Make runtests configurable.

Fix config issues and revert previous fixes for semi-colon issues

Added an option to make pch enabled in Cmake

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.

This reverts commit 41261d95.
This reverts commit 7c9accb6.

Instead of trying to work around all of the potential semicolon issues
in glslang, making it conform to Chromium's style, mark the code
explicitly as non-chromium in the BUILD.gn, so chromium doesn't
attempt to enforce its style rules on glslang.

Fixes #1931

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.