Some binutils versions will drag in an object to satisfy the entry
symbol; some won't.  Try to cope with this exciting variety of
behaviour by ensuring that all entry symbols are unique.

Remove the explicit inclusion of the prefix object on the linker
command line, since the entry symbol now provides all the information
needed to identify the prefix.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Use -ffunction-sections, -fdata-sections, and --gc-sections to
automatically prune out any unreferenced sections.

This saves around 744 bytes (uncompressed) from the rtl8139.rom build.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add makefiles, ld scripts and default config for linux platform for
both i386 and x86_64.

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>