make str_len an alias for strlen when on diet libc

str/str_len.c

@@ -1,5 +1,8 @@
 #include "str.h"
 
+#ifdef __dietlibc__
+unsigned int str_len(const char* in) __attribute__((alias("strlen")));
+#else
 unsigned int str_len(const char* in) {
   register const char* t=in;
   for (;;) {
@@ -10,3 +13,4 @@ unsigned int str_len(const char *in) {
   }
   return t-in;
 }
+#endif