Previously, this code would fail to detect glibc version because it
relied on libc.so.6 being a symlink which revealed the answer. On modern
distros, this is no longer the case.
This new strategy finds the path to libc.so.6 from /usr/bin/env, then
inspects the .dynstr section of libc.so.6, looking for symbols that
start with "GLIBC_2.". It then parses those as semantic versions and
takes the maximum value as the system-native glibc version.
closes#6469
see #11137closes#12567
fa940bafa2