on win64, use SEH unwind tables to walk callstack

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on May 08, 2013 22:42:06_

With the common lack of frame pointers for win64 code, we should use the
SEH unwind tables to construct callstacks.

I'm seeing a lot of callstack issues with extra frames on win64 with
-replace_malloc, and this is one solution.

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=1222_

Start by locating the win64 callstack construction and the handling of -replace_malloc, then read how existing frame walking works. Investigate the SEH unwind tables and define completion as producing callstacks without the reported extra frames on win64; the issue names no specific files or tests.

Written by the indexing model from the issue text.