marl::blocking_call() calls the passed function on another thread.
Attempting to unlock a mutex on a different thread that locked it is
illegal.

Also lock for destruction.

Bug: b/140421726
Change-Id: I87226176bc3a1a454d9c79a139f4d42e51f66814
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/43908Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>