swift234

[sourcekit] Synchronize cursor-info requests on generated interfaces

Cursor info requires access to the underlying AST, which is not
thread-safe. This manifest as crashes when performing concurrent
cursor-info requests on the same generated interface. We already
prevented concurrent cursor-infos on regular Swift files by using the
ASTManager, but generated interfaces use the InterfaceGenContext which
may use either an ASTUnit or its own internal CompilerInstance.

rdar://problem/27311624