After adopting the stable/20221013 clang branch, ClangImporter started seeing out-of-date identifiers in macros where it previously never had. Force these identifiers to update themselves before we read the macro definition out of them.
Fixes rdar://104456939.
When apple/swift#39664 moved the logic for generating anonymous fields' names from ImportDecl to ImportName, it inadvertently replaced a check that the decl was *precisely* `clang::FieldDecl` with a check that it was `FieldDecl` *or a subclass*. This could cause a crash when it tried to call `FieldDecl::getFieldIndex()`, which doesn't work properly on instance variables even though `ObjCIvarDecl` is a subclass of `FieldDecl`. The easiest way to reproduce this is to use a bit field in a class's instance variables, since clang inserts an anonymous instance variable after it for padding.
This commit adds a test of a bit field instance variable and fixes the bug. It also adds a PrettyStackTrace frame in the Swift lookup table preparation code, which should make other bugs like this easier to diagnose.
Fixes rdar://85173321.
