[libc] fix more readability-identifier-naming lints (#83914)
Found via:
$ ninja -k2000 libc-lint 2>&1 | grep readability-identifier-naming
Auto fixed via:
$ clang-tidy -p build/compile_commands.json \
-checks="-*,readability-identifier-naming" \
<filename> --fix
This doesn't fix all instances, just the obvious simple cases where it makes
sense to change the identifier names. Subsequent PRs will fix up the
stragglers.