[lldb] Report old modules from ModuleList::ReplaceEquivalent

This allows the Target to update its module list when loading a shared
module replaces an equivalent one.

A testcase is added which hits this codepath -- without the fix, the
target reports libbreakpad.so twice in its module list.

Reviewed By: jingham

Differential Revision: https://reviews.llvm.org/D89157

(cherry picked from commit d20aa7ca)