tree-wide: unify some code that looks for --help in the command line

src/basic/process-util.h

@@ -191,3 +191,5 @@ int setpriority_closest(int priority);
 bool invoked_as(char *argv[], const char *token);
 
 _noreturn_ void freeze(void);
+
+bool argv_looks_like_help(int argc, char **argv);