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.
ditto