util: Declare a cleanup routine for a cpu_set_t

Make use of it in config_parse_cpu_affinity2.

Tested by tweaking the `CPUAffinity' setting in /etc/systemd/system.conf
and reloading the daemon to confirm it is working as expected.

No regressions observed in test cases.

src/basic/util.h

@@ -363,6 +363,9 @@ int fd_is_temporary_fs(int fd);
 
 int pipe_eof(int fd);
 
+DEFINE_TRIVIAL_CLEANUP_FUNC(cpu_set_t*, CPU_FREE);
+#define _cleanup_cpu_free_ _cleanup_(CPU_FREEp)
+
 cpu_set_t* cpu_set_malloc(unsigned *ncpus);
 
 #define xsprintf(buf, fmt, ...) assert_se((size_t) snprintf(buf, ELEMENTSOF(buf), fmt, __VA_ARGS__) < ELEMENTSOF(buf))