These variables really are local variables -- they have have a
TopLevelCodeDecl as their DeclContext rather than the SourceFile.
Treating them as global variables caused crashes in serialization.
We need an overhaul of top-level variables in script files anyway
(see rdar://problem/20992489&21628526), but this fixes the immediate
issue.
rdar://problem/21928533
Swift SVN r30519
