Add Makefile support for DSBT ELF.

Add Makefile support for DSBT ELF.

This adds support for a new binary format, DSBT ELF, to the Makefiles.
Every shared library is assigned a DSBT index, and the link.so macro is
adjusted to ensure the correct linker argument is passed.

Configuration and ldso support will follow in separate commits.

Signed-off-by: Bernd Schmidt <bernds@codesourcery.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>