Here is the version reported by the libc on an embedded Linux system (i.e not a
Linux distro) without any package manager:
# /lib/libc.so.6
GNU C Library (Buildroot) stable release version 2.26, by Roland McGrath et al.
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 7.2.0.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC
For bug reporting instructions, please see:
<http://www.gnu.org/software/libc/bugs.html>.
So without any help from the build system, we can't say what's the libc version.
This can be ether the official Glibc 2.26 release or the glibc-2.26-58-gf725563.