[scudo][standalone] Add string utility functions
Add some string utility functions, notably to format strings, get
lengths, convert a string to a number. Those functions will be
used in reports and flags (coming up next). They were mostly borrowed
Make use of the string length function in a couple places in the
platform code that was checked in with inlined version of it.
Add some tests.
Reviewers: morehouse, eugenis, vitalybuka, hctim
Reviewed By: morehouse, vitalybuka
Subscribers: mgorny, delcypher, jdoerfert, #sanitizers, llvm-commits
Tags: #llvm, #sanitizers
Differential Revision: https://reviews.llvm.org/D59262