Default to using threads. This doesn't affect the normal release build.

Define -DMODULAR in Makefile.rump instead of the sys/rump/librump
Makefile.inc so that it gets picked up by UPDATE=1

Define MODULAR for rump core components. This enables module
loading via the kernel module framework (instead of dlopen()).
For now it only works on amd64 and i386, but for the rest it should
just b

Define MODULAR for rump core components. This enables module
loading via the kernel module framework (instead of dlopen()).
For now it only works on amd64 and i386, but for the rest it should
just be a matter of including the relevant kobj_machdep.c modules
from the kernel sources.

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fix compilation and lint warnings.

Specify RUMP_WITHOUT_THREADS only in one place.