Update LLDB to use LLVM's DynamicLibrary.

LLDB had implemented its own DynamicLibrary class for plugin
support.  LLVM has an equivalent mechanism, so this patch deletes
the duplicated code in LLDB and updates LLDB to reference the
mechanism provided by LLVM.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@216606 91177308-0d34-0410-b5e6-96231b3b80d8
Create a HostProcess class.

This is a lightweight wrapper around a pid.  It is intended to be
lightweight enough to serve as a replacement anywhere we currently
store a pid.  It provides convenience methods and common process
operations.

This patch does not yet make use of HostProcess anywhere.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@216607 91177308-0d34-0410-b5e6-96231b3b80d8