Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Remove PAGE_SIZE from libthr

In libthr we use PAGE_SIZE when allocating memory with mmap and to check
various structs will fit into a single page so we can use this allocator
for them.

Ask the kernel for the page size on init for use by the page allcator
and add a new machine dependent macro to hold the smallest page size
the architecture supports to check the structure is small enough.

This allows us to use the same libthr on arm64 with either 4k or 16k
pages.

Reviewed by: kib, markj, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34984

libthr: Use <machine/tls.h> for most MD TLS details.

Note that on amd64 this effectively removes the unused tcb_spare field
from the end of struct tcb since the definition of struct tcb in
<x86/tls.h> does not include that field.

Reviewed by: kib, jrtc27
Sponsored by: The University of Cambridge, Google Inc.
Differential Revision: https://reviews.freebsd.org/D33352

libthr: Remove the DTV_OFFSET macro.

This macro is confusing as it is not related to the similarly named
TLS_DTV_OFFSET. Instead, replace its one use with the desired
expression which is the same on all platforms.

Reviewed by: kib, emaste, jrtc27
Sponsored by: The University of Cambridge, Google Inc.
Differential Revision: https://reviews.freebsd.org/D33345

RISC-V: Fix an alignment warning in libthr

Compiling with clang gives a loss-of-alignment error due the cast to
uint8_t *. Since the TLS is always tcb aligned and TP_OFFSET is defined
as sizeof(struct tcb) we can guarantee there is no misalignment. Silence
the error by moving the offset into the inline assembly.

Reviewed by: br
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D21926

libthr: fix warnings at WARNS=6

Fix more warnings about redundant declarations.

Reviewed by: kib emaste
MFC after: 3 days
Sponsored by: Dell EMC
Differential Revision: https://reviews.freebsd.org/D10932

Unmagic the thread pointer offset.

Add pthread MD part for RISC-V.

Reviewed by: andrew
Sponsored by: DARPA, AFRL
Sponsored by: HEIF5
Differential Revision: https://reviews.freebsd.org/D5063