Use libc version as a collation version on glibc systems.
Using glibc's version number to detect potential collation definition
changes is not 100% reliable, but it's better than nothing.
Author: Thomas Munro
Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/
4b76c6d4-ae5e-0dc6-7d0d-
b5c796a07e34%402ndquadrant.com