Implemented fclose() and strrchr()

photon/libc/string/strrchr.c

@@ -0,0 +1,15 @@
+#include <string.h>
+
+char *strrchr(const char *s, int c)
+{
+    /* include null term */
+    long sz = strlen(s) + 1;
+
+    for (long i = sz; i >= 0; i--) {
+        if (s[i] == c) {
+            return (char *)(s + i);
+        }
+    }
+
+    return NULL;
+}