And, properly treat imports as per-file: when looking up decls through the
TU module, don't pick up every other source file's imports.
This implements our resolution rules:
1. Check the current source file.
2. Check the current module.
3. Check imported modules.
Currently, "import Foo" is treated as a file-private import and
"@reexported import Foo" is treated as a public /and/ module-wide import.
This further suggests that access control is the right tool for re-export
control:
(private) import Foo // current file only
package import Foo // whole module
public import Foo // whole world
Swift SVN r9682
and remove DeclContext base class from FuncDecl, ConstructorDecl and
DestructorDecl
This decreases the number of DeclContexts to 7 and allows us to apply
alignas(8) to DeclContext.
Swift SVN r8186
