Just provide a "(null)" literal in case driverName is NULL.
In file included from ../src/glx/dri3_glx.c:76: ../src/glx/dri3_glx.c: In function ‘dri3_create_screen’: ../src/glx/dri_common.h:70:36: error: ‘%s’ directive argument is null [-Werror=format-overflow=] 70 | #define CriticalErrorMessageF(...) dri_message(_LOADER_FATAL, VA_ARGS) | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ../src/glx/dri3_glx.c:1002:4: note: in expansion of macro ‘CriticalErrorMessageF’ 1002 | CriticalErrorMessageF("failed to load driver: %s\n", driverName); | ^~~~~~~~~~~~~~~~~~~~~ ../src/glx/dri3_glx.c:1002:50: note: format string is defined here 1002 | CriticalErrorMessageF("failed to load driver: %s\n", driverName); | ^~ cc1: some warnings being treated as errors