Whole-line sequence points

[tmat]

Managed C++ generates whole line sequence points as (line, 0, line, 0), which isn't compatible with Portable PDB requirements on sequence point. The Pdb2Pdb converter converts these to (line, 0, line, 0xffff). we might want SymReader to present these back as (line, 0, line, 0).

If Managed C++ compiler ever generated Portable PDBs, it should fill in columns properly.