Using glibc's version string to detect potential collation definition
changes is not 100% reliable, but it's better than nothing.  Currently
this affects only collations explicitly provided by "libc".  More work
will be needed to handle the default collation.

Author: Thomas Munro, based on a suggestion from Christoph Berg
Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/4b76c6d4-ae5e-0dc6-7d0d-b5c796a07e34%402ndquadrant.com