Test: Use a xvfb wrapper for x11 test The x11 test is currently silently skipped in CI, because it requires a running X server. Create a xvfb wrapper to run the test. We do not use `xvfb-run`, because it is a shell script and it causes valgrind to detect unrelated memory issues in the shell (dash, bash). Improve wrapper using a special ELF section TODO: The wrapper is intended to be used with the x11comp test as well.