Add support to read aux vector values

Summary:
This is the second patch to improve module loading in a series that started here (where I explain the motivation and solution): https://reviews.llvm.org/D62499

I need to read the aux vector to know where the r_debug map with the loaded libraries are.
The AuxVector class was made generic so it could be reused between the POSIX-DYLD plugin and NativeProcess*. The class itself ended up in the ProcessUtility plugin.

Reviewers: clayborg, xiaobai, labath, JDevlieghere

Reviewed By: clayborg, labath, JDevlieghere

Subscribers: emaste, JDevlieghere, mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D62500

llvm-svn: 363098