As you know due to some problems with Clang7, Mesa on x64 was recently compiled with GCC.
Usage Mesa compiled with Clang caused a black screen on old systems like AMD CPU from Athlon II / Phenom II era and some Intel too (machines without AVX instruction). More info here: https://issues.openmandriva.org/show_bug.cgi?id=2381
It seems that the upgrade of Clang to version 8 has fixed this problem.
That’s it for me. The update has fixed this. But you have to confirm it.
You can download test mesa release from here
dnf config-manager --add-repo=http://abf-downloads.openmandriva.org/cooker/container/23628/x86_64/main/release/
and run update
dnf clean all && dnf update --nogpgcheck