Fix build with clang 6

/wrkdirs/usr/ports/devel/powerpc64-gcc/work/gcc-6.3.0/gcc/ubsan.c:1474:20: error: comparison between pointer and integer ('const char *' and 'int')

|| xloc.file == '\0' || xloc.file[0] == '\xff'
   ~~~~~~~~~ ^  ~~~~

PR: 224669
Reported by: pkg-fallout