Add memcmp(), clean up bochsrc.txt

kernel/libk/string.c

@@ -60,3 +60,16 @@ usize_t strlen(const char *str) {
   for (s = str; *s; ++s);
   return (s - str);
 }
+
+int memcmp(const void *s1, const void *s2, usize_t n) {
+  unsigned char *p = (unsigned char *)s1;
+  unsigned char *q = (unsigned char *)s2;
+
+  while (n--) {
+    if (*p != *q) {
+      return (int)*p - (int)*q;
+    }
+    p++, q++;
+  }
+  return 0;
+}