bug#57346: undeclared identifier 'CLOCK_MONOTONIC'

[Po Lu]

Glenn Morris <rgm@gnu.org> writes:

> Package: emacs
> Version: 29.0.50
>
> OS X Clang build failing for three weeks. Ref:
> https://hydra.nixos.org/build/186116177
> https://hydra.nixos.org/build/188132926
>
> xterm.c:6659:3: warning: implicit declaration of function
> 'clock_gettime' is invalid in C99 [-Wimplicit-function-declaration]
>   clock_gettime (CLOCK_MONOTONIC, &time);
>   ^
> xterm.c:6659:18: error: use of undeclared identifier 'CLOCK_MONOTONIC'
>   clock_gettime (CLOCK_MONOTONIC, &time);

Right, the internet says OS X doesn't have clock_gettime.

Does gnulib provide it? Failing that, I'd rather just make vsync
conditional on clock_gettime being available, since the mechanism it
uses cannot possibly work on OS X.