new type: ptraddr_t

ptraddr_t is an unsigned integer type that can hold the address of any
pointer.  It differes from uintptr_t in that it does not carry
provenance which is useful for CHERI in that it can disambigurate the
provenance of uintptr_t expressions.  It differes from size_t in that
some segmented architecture (not supported by FreeBSD) may have a size_t
that does not hold an address.

ptraddr_t is not yet standardized, but is currently proposed for
inclusion in C++2Y.

Prefer the compiler defined __PTRADDR_TYPE__ defintion where available
as this a new type and we don't need to worry about historical values.
Fall back to __size_t where unavailable.

Reviewed by:	kib, markj
Effort:		CHERI upstreaming
Sponsored by:	Innovate UK
Differential Revision:	https://reviews.freebsd.org/D53817

share/man/man7/arch.7

@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd October 1, 2025
+.Dd November 27, 2025
 .Dt ARCH 7
 .Os
 .Sh NAME
@@ -48,7 +48,8 @@ and later, unless otherwise noted.
 .Fx
 uses a flat address space.
 Variables of types
-.Vt unsigned long
+.Vt unsigned long ,
+.Vt ptraddr_t ,
 and
 .Vt size_t
 have the same representation.