Add support for Win64 stack unwind data as STACK CFI

This is a copy of https://breakpad.appspot.com/1264002/ where code review took place.

See https://bugzilla.mozilla.org/show_bug.cgi?id=548035 and https://code.google.com/p/chromium/issues/detail?id=115922

Credit to Mikhail I. Izmestev <izmmishao5@gmail.com> for original patch in https://breakpad.appspot.com/345002/

BUG=572
TEST=Run dump_syms_unittest after compiling dump_syms_regtest.cc with x64 toolchain
R=mark@chromium.org

Review URL: https://breakpad.appspot.com/1274002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1290 4c0a9323-5329-0410-9bdc-e9ce6186880e