Fixed some issues with parsing C++ methods where our detection

was failing if the DWARF was laid out in a certain way. The way
we detect C++ classes is now more robust so that a class method
can be defined outside of the class and refer to a definition inside
the class with a DW_AT_specification or DW_AT_abstract_origin attribute.

Fixed a case in Thread.cpp where we were looking up info in the frame
when we didn't need to. This was from some changes to support external
editors. Now the info is only looked up if needed.

llvm-svn: 137436