lang/ruby2[345]: Improve qsort_r() detection

[ed]

Summary

This change merges the following upstream pull request into the Ruby
interpreter ports:

https://github.com/ruby/ruby/pull/1954

Adding this patch to these ports will ensure that once we patch up
qsort_r() to be compatible with glibc, Ruby will automatically pick them
up. Ruby should also build fine without this patch, but this will cause
it to use its own implementation, which blows up the binary size
slightly. See FreeBSD bug #231256 and Phabricator review D17083 for
details.

Test Plan

Poudriere runs seem to pass for 11.x amd64. Logs indicate that this
doesn't negatively affect the existing qsort_r() detection:

checking whether qsort_r is GNU version... no
checking whether qsort_r is BSD version... yes

[sunpoet]

LGTM. Thanks!