We have a legacy dependency of libjvm to librt for the clock_* functions :
https://github.com/openjdk/jdk/blob/f993f90c86f89eb0c7f42ebecb45a68eae0bd9ea/make/autoconf/libraries.m4#L139

But this is for very old systems with distros like RHEL 6 or SLES11 with glibc 2.16 or older, where the clock_ functions were still in librt ; but those ancient distros play no role any more for current JDK26.
On the other hand, we now use the timer_* functions from librt e.g. in JFR and these are in librt so the comment should be adjusted.