[libc] Add strtol, strtoul, and strtoull

Authored by michaelrj on Aug 12 2021, 2:34 PM.


[libc] Add strtol, strtoul, and strtoull

Updates the internal string conversion function so that it
uses the new Limits.h added in a previous commit for max and min values,
and has a templated type. This makes implementing the other strto*
functions very simple.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D107999