Hi -
I've just removed all old signal delivery support (sigcontext with libc
trampoline, sigcontext with uao/stack trampoline) for native (64-bit)
code from the kernel.
This code was compiled in for COMPAT_16 kernels. There was no 1.6 release
for amd64, so there is no point in keeping and maintaining it, let alone
performance implications.
COMPAT_16 is only useful in combination with COMPAT_NETBSD32, to run
NetBSD-1.6/i386 binaries. Kernel configurations defining the former without
the latter will just not build.

best regards
Matthias