This path implements missing case in PdbAstBuilder::CreateType for LF_MFUNCTION. This is necessary, for example, in stack unwinding of struct methods.
Please add some detail to the commit message and consider re-titling it. It looks like this patch is actually adding missing functionality rather than "fixing" a bug in how structs are handled. If that's correct, then please make the commit message reflect that.
Sorry I didn't get a chance to finish reviewing this today, but I'll try to get it done tomorrow.
Looks like this is failing on the windows bot http://lab.llvm.org:8011/builders/lldb-x64-windows-ninja/builds/4635/steps/test/logs/stdio.
Looking at the test, it seems that you are asserting that you will unwind into a particular offset in ntdll.dll. That sounds like an incredibly fragile assertion, which will only be true for people running the exact same version of ntdll that you happen to have...