[scudo][standalone] Add a standalone vector class

Summary:
This CL adds a standalone vector class that will be used by the scoped
strings when they land. We reimplement our own vector class because we
can't use the std library one.

It's mostly borrowed from the current sanitizer_common one, with LLVM
code style changes.

Additionnally a casing change in a function name that slipped through
the previous review (the function isn't used yet).

Reviewers: vitalybuka, eugenis, flowerhack, dmmoore415, mcgrathr, morehouse

Reviewed By: vitalybuka

Subscribers: mgorny, delcypher, #sanitizers, llvm-commits

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D58689

llvm-svn: 354999