Make sure session is initialized before it is used by objectLayer.
Fixes assert related to objectLayer using an invalid
std::recursive_mutex in the session instance.

Also added an explicit resource removal to fix assert in
~RTDyldObjectLinkingLayer().

Bug: b/171402030
Change-Id: I4f628a9ed4afd0126462858f8f0e3e42f90e21b3
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/49508
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>