strverscmp: I forgot to export it

Result was:

strverscmp.o:
000000ec T __GI_strverscmp

i.e. no plain "strverscmp"!

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

libc/string/strverscmp.c

@@ -115,3 +115,4 @@ int strverscmp (const char *s1, const char *s2)
       return state;
   }
 }
+libc_hidden_def(strverscmp)