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

Disable support for compat syscalls on arm64. These symbols were never
shipped since arm64 exists only on 11+.

Submitted by: brooks
Reviewed by: emaste, imp

Add include for declaration of _set_tp(). Eliminates -Wmissing-prototypes warnings.

Add the definitions of __infinity and __nan.

Add support for makecontext. This supports up to 8 arguments as this
simplifies the code, these can be passed in registers.

Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation

Implement fpgetmask, it's needed by Python.

Approved by: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation

Implement fpsetmask. Some third-party software makes use of it, for example
perl.

Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation

Set the alignment of the setjmp magic values correctly. The alignment needs
to be before the lavel, otherwise an extra word may be added between the
label and the data.

Obtained from: ABT Systems Ltd
Sponsored by: The FReeBSD Foundation

Set the correct register when calling sigprocmask in longjmp.

Submitted by: Patrick Wildt <patrick@bitrig.org>
Obtained from: drahn@bitrig.org

Add fabs() to arm64 libc

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D2532

Add the start of libc and libstand for arm64. Not all of the machine
dependent functions have been implemented, but this is enough for world.

Differential Revision: https://reviews.freebsd.org/D2132
Reviewed by: emaste
Sponsored by: The FreeBSD Foundation