[libc][NFC] Make test macros callable from helper methods of test classes.

This is acheived by making the RunContext a state variable of the test
classes.

Reviewed By: lntue

Differential Revision: https://reviews.llvm.org/D90805

GitOrigin-RevId: 0e3532da98c5aa62582eee9cca07aaf5844b0b90
2 files changed