Qt WebEngine is skipped in current CentOS 7 linux builds

Commit e781377d2c1582ff358aeabdaf75d77db94fd71c in qtwebengine.git increased the required glibc version from 2.17 to at least 2.27. CentOS 7 with devtoolset-4 only offers gcc 5.3.1 and glibc 2.17. Therefore, WebEngine is currently skipped on that configuration.

Since this is the configuration that the linux packages for release get built on, it means we have to fix this for 5.13.1. The two options are basically trying to lower the version requirement somehow or upgrading glibc / the compiler toolchain.

Somewhat connected to QTBUG-76329 as that is also caused by a malfunction in 5.3.1 that is fixed in later versions.