[libc] Surround get_start_args_addr in __llvm_libc namespace.

Summary: Caught by libc-tidy from patch D77281.

Reviewers: sivachandra

Reviewed By: sivachandra

Subscribers: tschuett, libc-commits

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D78700

GitOrigin-RevId: d94af364acfa252ef980bc18a53fdf01dceea201
1 file changed