std.c: Make clock_nanosleep available on serenity

Follow-up to https://codeberg.org/ziglang/zig/pulls/30746.

The TIMER_ABSTIME value was adjusted to match other systems in
https://github.com/SerenityOS/serenity/pull/26543.
27039a014cLinus Groh committed on 1/9/2026, 8:37:49 AM· committed by Andrew Kelleyparentb929078
1 file changedLine totals unavailable