Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

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

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.

/* -> /*- for license, minor formatting changes

- use symbol for user-context offset
- fix szsigcode size declaration

Approved by: benno

- Rename the _C_LABEL macro to CNAME.
- Rename the _ASM_LABEL macro to ASMNAME.
- Add the HIDENAME macro which is used in libc's syscall stuff.

Commit of stuff that's been sitting in my tree for a while.

Highlights include:
- New low-level trap code from NetBSD. The high level code still needs a lot
of work.
- Fixes for some pmap handling in thread switching.
- The kernel will now get to attempting to jump into init in user mode. There
are some pmap/trap issues which prevent it from actually getting there though.

Obtained from: NetBSD (parts)