[lldb] Add a test for user-defined objc_copyRealizedClassList_nolock

LLDB evaluates some utility expression to update the Objective-C class list that
ends up calling function such as `free` or `objc_copyRealizedClassList_nolock`.
This adds a test that just tries to define our own bogus version of
`objc_copyRealizedClassList_nolock`. It just tests that LLDB doesn't crash as we
currently don't have a way to tell LLDB to look for the function in a specific
library.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D107778