configure: make call to readlink portable to non-GNU (BSD) systems

The argument '-e' for readlink is a GNU extension.
In setting the variable 'where' the argument '-e' is not necessary, thus eliminated.

 --- binutils/ld/ldmain.c

 +++ binutils/ld/ldmain.c

 @@ -293,2 +293,3 @@ main (int argc, char **argv)

    link_info.combreloc = TRUE;

 +  link_info.relro = TRUE;

    link_info.strip_discarded = TRUE;