Objective-C method unintended override checking is one such case where
properly checking unintended overrides requires us to essentially look
at the whole module, because one translation unit may declare
something that produces an Objective-C method "setFoo:" in a
superclass while another translation unit declares something with a
distinct name that produces an Objective-C method "setFoo:". So, when
we don't have a primary file (e.g., when we're doing the merge-module
step), delay such checks until after all the source files for the
module have been type-checked. When there is a primary file, we
perform the checking that we can based on type checking that primary
file (and whatever got touched along the way), so we get a subset of
the proper diagnostics.
Swift SVN r23179
In order to implement immediate and REPL modes in swift_driver, this functionality
needs to be in a library (instead of directly in the swift executable).
Swift SVN r12519
