swift234

Use the conformance lookup table to find protocol conformances.

Replace the loop over all known protocols with a query into the
actual conformance lookup table, which more properly deals with
out-of-order conformance queries, inheritance of protocol
conformances, and conformance queries in multi-file situtations.

The SILGen test change is because we're no longer emitting redundant
conformances, while the slight diagnostic regression in
circular-inheritance cases is because we handle circular inheritance
very poorly throughout the compiler.

While not the end, this is a major step toward finishing
rdar://problem/18448811.

Swift SVN r26299