libcrypt: add missing errno.h header

Fixes:
libcrypt/crypt.c:29:15: error: 'EINVAL' undeclared (first use in this function)
   __set_errno(EINVAL);
               ^~~~~~

Signed-off-by: Yann Sionneau <ysionneau@kalray.eu>

libcrypt/crypt.c

@@ -6,6 +6,7 @@
 
 #include <unistd.h>
 #include <crypt.h>
+#include <errno.h>
 #include "libcrypt.h"
 
 char *crypt(const char *key, const char *salt)