[PDB] Fill in "Parent" and "End" fields of scope-like symbol records

Summary:
There are a variety of records that open scopes: function scopes, block
scopes, and inlined call site scopes. These symbol records contain
Parent and End fields with the offsets of other symbol records. The End
field contains the offset of the matching S_END or S_INLINESITE_END
record. The Parent field contains the offset of the parent record, or 0
if this is a top-level scope (i.e. a function).

With this change, `llvm-pdbutil pretty -all` no longer crashes on PDBs
produced by LLD. I haven't tried a real debugger yet.

Reviewers: zturner, ruiu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34898

llvm-svn: 307278