Fixed a problem where LLDB inserted regular C

FunctionDecls into classes if it looked up a
method in a different DWARF context than the
one where it found the parent class's definition.

The symptom of this was, for a method A::B(),

1) LLDB finds A in context 1, creating a
   CXXRecordDecl for A and marking it as needing
   completion

2) LLDB looks up B in context 2, finds that its
   parent A already has a CXXRecordDecl, but can't
   find a CXXMethodDecl for B

3) Not finding a CXXMethodDecl for B, LLDB doesn't
   set the flag indicating that B was resolved

4) Because the flag wasn't set, LLDB's fallthrough
   code creates a FunctionDecl for B and sticks it
   in the DeclContext -- in this case, A.

5) Clang crashes on finding a FunctionDecl inside a
   CXXRecordDecl.

llvm-svn: 154627