[Interest] Minimal glibc version for Qt 5.15.9

[Marius Kittler]

Hi,

I don't know the minimum required glibc version of Qt. I recently compiled Qt 
6.3.0 against glibc 2.26 (at least qtbase, qtdeclarative, qtwayland and a few 
more repos) and it worked just fine. Likely it builds against even lower 
versions of glibc as well. I suppose you'll have to test it yourself. Since 
you've mentioned Ubuntu 18.04 specifically: I've already tested my build on 
that particular OS and they worked, as well as on openSUSE Leap 15.3 and an 
up-to-date Arch Linux system. So it is certainly possible to support that OS 
using the latest Qt 6 release and surely the same applies to Qt 5.

Note that if you build Qt (or any other library) against a certain glibc 
version than that is the minimum required glibc version of that specific build. 
Additionally, you also need to build all dependencies in your stack (e.g. also 
dependencies of Qt itself, and the dependencies of that dependencies and so 
on) against that older glibc version. Of course that doesn't count for 
dependencies used only at build time, e.g. I could use Arch Linux's recent 
LLVM/Clang build to link tools from qttools against (in a quite hacky way, but 
it worked). (Further more obvious examples of build-only tools are of course 
binutils, CMake, Meson and autotools. However, GCC needs to be built against 
the older glibc as it contains libstdc++ which is required at runtime.)

By the way, these are the build scripts I used to conduct builds against glibc 
2.26 (under Arch Linux):
https://github.com/Martchus/PKGBUILDs#static-gnulinux-libraries=

Best Regards
Marius