iOS 8 does not support `thread_local`, which is still in use.
Another approach will have to be found.

This change is a revert of the following changes:

a3845240 - "Simplify PoolAlloc with use of thread_local."
abf92c80 - "Deprecate InitializeDll functions"
33585c87 - "Limit visibility of symbols for internal libraries"

Issue: #2346

Avoid spurious warning about uninit var

Update spirv-tools known-good to most recent stable

Add changes for SPV_EXT_shader_atomic_float_add

Limit visibility of symbols for internal libraries

Also remove `SPIRV/doc.cpp` from the `SPVRemapper` target as this
is part of `SPIRV`, causing ODR violations. Instead have
`SPVRemapper` link against `SPIRV`.

Fixes ODR violations.

Simplify PoolAlloc by using `thread_local`

also search global sequences for live variables

These were only used for TThreadPool, which now uses `thread_local`.

glslang is using C++ 11, which has first class support for variables of the `thread_local` storage class.

By dropping the use of the `OS_[GS]etTLSValue`, we can simplify the logic, and have it support a thread-local default allocator if none is provided.

Issue: #2346

Finalize glslang 10.15.3847, start glslang 11, drop support for VS2013

when traversing the AST to find live UBOs etc, also traverse
references to global module-level variables, incase they are
being filled in from UBOs etc.

This was scheduled for today - 20th July 2020.

Updates Appveyor configs to use VS2015 instead.

Update license-checker.cfg with simplified rules

`license-checker` has been updated to support `**` wildcards simplifying the ruless, and multiple license configs.

Add a new config for the bison generated files to ensure their licenses don't change.

Add new rules for update of license-checker

`license-checker` will be updated to support `**` based wildcards. As part of this, `license-checker` will now traverse into subdirectories that would previously be excluded when the parent directory is excluded.

This change adds new rules that work with both the old version and new, to ease migration.

GLSL/SPV: Propagaet precision qualifier from function to return value.

When a return value's type has no precision qualification (e.g., the return
expression is formed from a constructor), and the formal function return type
has a precision qualification, back propagate that from the return type to the
type of the return value's expression.

runtests: Check error codes, set LD_LIBRARY_PATH

`glslangValidator` will only return [the codes 0..6](https://github.com/KhronosGroup/glslang/blob/b481744aea1ecf52ee4591afaa0f5e270b9d1636/StandAlone/StandAlone.cpp#L117-L125). Fail the test if anything else is returned (like due to the exe crashing).

Also set `LD_LIBRARY_PATH` to contain the `lib` directory before calling glslang.

Kokoro: Print test output to stdout

Give build_info.py the executable bit

Fix recently found non-determinism with gl_WorldToObject3x4EXT.

CMake: Move project() to top of CMakeLists.txt

Add bison license to LICENSE.txt

This problem needs to be fixed, but in parallel, we need to see master
and any other changes to it passing all tests.

The removed test is ray-tracing centric, and may indicate non-determinism
in recent code added for that functionality.

Also remove `NOTICE` from message() about PCHs - it seems to print this in the actual message, contrary to the documentation where it is used as a severity.

Revert "Merge pull request #2330 from ShabbyX/optimize_for_angle"