util-lib: wrap personality() to fix up broken glibc error handling (#6766)

glibc appears to propagate different errors in different ways, let's fix
this up, so that our own code doesn't get confused by this.

See #6752 + #6737 for details.

Fixes: #6755

src/basic/process-util.h

@@ -91,6 +91,7 @@ bool oom_score_adjust_is_valid(int oa);
 unsigned long personality_from_string(const char *p);
 const char *personality_to_string(unsigned long);
 
+int safe_personality(unsigned long p);
 int opinionated_personality(unsigned long *ret);
 
 int ioprio_class_to_string_alloc(int i, char **s);