elf-core: Improve FreeBSD support and move data extraction to parse time

Extracting thread data at parse time simplifies multi-platform support.
This change adds FreeBSD thread names and auxv info.

Thanks to Samuel Jacob for review, testing, and improvements.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@186975 91177308-0d34-0410-b5e6-96231b3b80d8