I'm not excited by the idea of using hardcoded constants for getrandom(). There is a risk of using wrong constants depending on the architecture or the Linux kernel version.

The code is already very low-level: it calls directly the syscall using syscall() function. getrandom() has no nice glibc clean API yet:
https://sourceware.org/bugzilla/show_bug.cgi?id=17252

I suggest to close the issue as WONTFIX. It's ok to use a file descriptor and read /dev/urandom. getrandom() is nice to have, but it's not really a killer feature.

For Fedora: sure, you can use vendor patches to workaround your technical issue, builders using an old kernel :-) But it would be simpler to upgrade the builder, no? :-)