LibC: Add ru_maxrss to struct rusage

This is not required by posix but some ports use it

userspace/libraries/LibC/include/sys/resource.h

@@ -36,6 +36,7 @@ struct rusage
 {
 	struct timeval ru_utime; /* User time used. */
 	struct timeval ru_stime; /* System time used. */
+	long ru_maxrss;          /* Maximum resident set size (in kilobytes). */
 };
 
 #define RLIMIT_CORE		0