sys: Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

Rename assym.s to assym.inc

assym is only to be included by other .s files, and should never
actually be assembled by itself.

Reviewed by: imp, bdrewery (earlier)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D14180

Align signal stack pointer to 16 bytes.

The stack must be aligned to 16 bytes at all times. Clang 3.8 is especially
adamant about this, and causes strange behavior and segmentation faults if it is
not the case.

PR: kern/206810

Repair nested signal handling on PowerPC. The signal trampoline code
was not allocating space for the parameter save area in the stack frame.
If the compiler chose to save the argument to the signal handler on the
stack, it would overwrite the first 32 bits of the sigaction struct with
it, corrupting it for a subsequent invocation.

PR: powerpc/183040
MFC after: 8 days

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

MFppc64:

Kernel sources for 64-bit PowerPC, along with build-system changes to keep
32-bit kernels compiling (build system changes for 64-bit kernels are
coming later). Existing 32-bit PowerPC kernel configurations must be
updated after this change to specify their architecture.