fix issue 3657: add lexical scope to CodeView debug info

https://d.puremagic.com/issues/show_bug.cgi?id=3657

This pull request consists of two parts:
- save the end of a scope block during parsing 
- reconstruct life time information of variables from line information

This is implemented for Win32 only, but should be adaptable to Win64 pretty easily. I don't know about the other platforms, though.
Though this patch currently works for cv4 only, the scope information should be available for other debug formats, too. These are not limited to lines < 65536 (we have machine generated code in our company where it's really annoying that VS still has this limitation).