swift234

Add a test for serialization under optimizations.

This used to pull in SIL functions from the stdlib, then try to serialize
them out again. Michael's r20375 allowed us to distinguish local functions
with shared linkage from deserialized functions with shared (now
SharedExternal) linkage, and the existing logic in the serializer took
care of skipping them.

<rdar://problem/17567391>

Swift SVN r20415