Chrome supports Linux versions which don't come with a glibc library
which supports __cxa_thread_atexit_impl. This function is required for
destroying C++11 thread_local objects at thread exit.

The 'jit' and 'unmaterializedVariables' thread-local objects used by
Reactor are only needed between Function<> creation and Routine
acquisition, so replace them by explicitly managed raw pointers.

Bug: chromium:1074222
Bug: b/153803432
Change-Id: I0a92bdd30940048b9ce0c208d3a2c1a952091283
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/44428
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>