Add getrusage syscall for mac/darwin

The syscall number existed but the wrapper for calling it
did not. Also adds the RUsage struct to receive the data.

Naming is kept the same as in sys/linux

core/sys/darwin/darwin.odin

@@ -2,3 +2,27 @@
 package darwin
 
 Bool :: b8
+
+timespec :: struct {
+        seconds:      int,
+        microseconds: int,
+}
+
+RUsage :: struct {
+        utime:         timespec,
+        stime:         timespec,
+        maxrss_word:   int,
+        ixrss_word:    int,
+        idrss_word:    int,
+        isrss_word:    int,
+        minflt_word:   int,
+        majflt_word:   int,
+        nswap_word:    int,
+        inblock_word:  int,
+        oublock_word:  int,
+        msgsnd_word:   int,
+        msgrcv_word:   int,
+        nsignals_word: int,
+        nvcsw_word:    int,
+        nivcsw_word:   int,
+}