Handle mipsn64

branches: 1.9.2;
Build the netbsd32_syscall module if mips64.
Don't build the linux_syscall module if mips*

branches: 1.8.10;
Add syscall_linux back for other arm architectures (accidently removed
in previous)

dtrace: add support for aarch64

branches: 1.6.18; 1.6.22;
dtrace syscall for linux32

Add syscall provider build glue, unhooked.

branches: 1.4.14;
adapt the cyclic module and profile dtrace provider to netbsd.
for now, just hook the cyclic callback into hardclock().

branches: 1.3.4; 1.3.12; 1.3.22;
DTrace: Add the Function Boundary Trace (FBT) provider moduile. This
module instruments every function in the kernel with entry and exit
probes. These probes are true zero-effect probes in that they don't
exist in the code until they are enabled. The probes are enabled by
directly patching the function entry and exit points to make jumps into
the dtrace framework.
This gives us over 29,000 trace points in the kernel.

branches: 1.2.2;
DTrace: Add an SDT (Statically Defined Tracing) provider framework, and
implement most of the proc provider. Adds proc:::create, exec,
exec_success, exec_faillure, signal_send, signal_discard, signal_handle,
lwp_create, lwp_start, lwp_exit.

DTrace: add the dtrace module.