swift234

[deserialization] Disable deserialization of vtables/witness tables for now.

Some recent work done by John have unblocked deserialization of SILFunctions. We
still can not properly deserialize witness tables/vtables but enabling by
default deserialization of SILFunctions from the stdlib is a good first step
toward reaching our performance goals.

There will be forthcoming commits which removes Benchmarks.swift and all of the
infrastructure we have in place for compiling benchmarks in the standard
library.

Swift SVN r14750