Changes to support the kernel linker:

Add a -Bforcedynamic option which generates a dynamic object even
if no shared libraries were given in the link.

Make RRS in text section warnings conditional on "-assert pure-text"
so that I can link non-PIC kernel modules without tons of link
errors. Changes to bsd.lib.mk to follow.

Fix a couple of bugs exposed by the fact that the kernel is not
linked at zero.

Reviewed by: jdp