swift234

[SIL] Don't assume we always have an associated DeclContext. (#2730)

...in code that I wrote. The integrated REPL, deprecated though it may
be, does not have an associated DeclContext because its SourceFile is
not considered complete. (The proper LLDB REPL does not suffer from
this problem because they use a new SourceFile for every block of
input.)

Elsewhere, tighten up code that may have hit similar bugs, though we
haven't seen anything hit these yet.

rdar://problem/26476281