[LLDB] OpenBSD support

[LLDB] OpenBSD support

Summary:
Add basic OpenBSD support. This is enough to be able to analyze core dumps for OpenBSD/amd64, OpenBSD/arm, OpenBSD/arm64 and OpenBSD/i386.

Note that part of the changes to source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp fix a bug that probably affects other platforms as well.  The GetProgramHeaderByIndex() interface use 1-based indices, but in some case when looping over the headers the, the loop starts at 0 and misses the last header.  This caused problems on OpenBSD since OpenBSD core dumps have the PT_NOTE segment as the last program header.

Reviewers: joerg, labath, krytarowski

Reviewed By: krytarowski

Subscribers: aemerson, emaste, rengolin, srhines, krytarowski, mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D31131

llvm-svn: 298810