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.

 reporter_name="unknown"

 reporter_url="http://iphonelinux.org/index.php/Glibc_toolchain_using_crosstool-NG"

 reporter_comment="An (experimental) toolchain targeting the Apple's iPhone."