Convert the TargetTransformInfo from an immutable pass with dynamic

Convert the TargetTransformInfo from an immutable pass with dynamic
interfaces which could be extracted from it, and must be provided on
construction, to a chained analysis group.

The end goal here is that TTI works much like AA -- there is a baseline
"no-op" and target independent pass which is in the group, and each
target can expose a target-specific pass in the group. These passes will
naturally chain allowing each target-specific pass to delegate to the
generic pass as needed.

In particular, this will allow a much simpler interface for passes that
would like to use TTI -- they can have a hard dependency on TTI and it
will just be satisfied by the stub implementation when that is all that
is available.

This patch is a WIP however. In particular, the "stub" pass is actually
the one and only pass, and everything there is implemented by delegating
to the target-provided interfaces. As a consequence the tools still have
to explicitly construct the pass. Switching targets to provide custom
passes and sinking the stub behavior into the NoTTI pass is the next
step.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171621 91177308-0d34-0410-b5e6-96231b3b80d8