Fixed up sed invocation to work with newer linker scripts.

Also committed changes from previous patch set which removed redundant
mathinline.h file.

commit 7c8a6732
Author: Ulrich Drepper <drepper@redhat.com>
Date:   Sat Jan 31 00:21:15 2009 +0000

        * elf/Makefile (ld.so): Adjust the sed script to insert _begin in to
        newer linker scripts.