Revert d2594298b89d0fb8989cae3ebc8900e77b6aa478

As reported on irc:

```
17:51 <q> jvoisin, fortify-headers seems to be broken (on Alpine at least)
17:52 <q> Repeating the message from over-there:
17:52 <q> /usr/include/fortify/string.h: In function 'strncat':
17:52 <q> /usr/include/fortify/string.h:297:36: error: implicit declaration of function 'strnlen'; did you mean 'strlen'? [-Wimplicit-function-declaration]
17:52 <q> This is with a simple file that includes string.h and call strncat, built with c99 -O1 f.c
```

1 files changed, 3 insertions, 1 deletions

diff --git a/include/string.h b/include/string.h
index 10d071a..c1c24bc 100644
--- a/include/string.h
+++ b/include/string.h
@@ -208,7 +208,9 @@ _FORTIFY_FN(stpncpy) char *stpncpy(char * _FORTIFY_POS0 __d, const char *__s,
 #if __has_builtin(__builtin___stpncpy_chk) && FORTIFY_USE_NATIVE_CHK
         return __builtin___stpncpy_chk(__d, __s, __n, __fh_bos(__d, 0));
 #else
-        __fh_size_t max_len_s = strnlen(__s, __n);
+        __fh_size_t max_len_s = strlen(__s);
+        if (max_len_s > __n)
+                max_len_s = __n;
         if (__fh_overlap(__d, max_len_s, __s, max_len_s))
                 __builtin_trap();