We enable other syscalls by default. I do not know much about it but maybe it is a good idea to also enable this one?
The ebuild has ERROR_SIGNALFD which means it'll be a nasty experience if you have the option off in your kernel. But I don't know how common it is to have that on, or why it was optional (maybe it was made optional when it was new). Please do some research for things like this to make the bugs more useful.
