Initial support for native debugging of x86/x64 Windows processes

Summary: Thanks to Hui Huang and the reviewers for all the help with this patch.

Reviewers: labath, Hui, jfb, clayborg, amccarth

Reviewed By: labath

Subscribers: amccarth, compnerd, dexonsmith, mgorny, jfb, teemperor, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D63165

llvm-svn: 368759