P0891 Make strong_order a Customization Point!

[jensmaurer]

P0891R2 Make strong_order a Customization Point! (Gašper Ažman, Jeff Snyder)

https://issues.isocpp.org/show_bug.cgi?id=503

Quote from paper: "R2 of this paper is a merge of its R1 and Jeff Snyder’s P0863R1, and is synchronized with Barry Revzin’s" P1186R1 #142.

[tituswinters]

LEWG in Kona:
We want to make strong_order (and friends) customization points (not strong_equals / weak_equals, those would be pessimizations, those APIs are removed).
SF F N A SA
2 8 1 0 1

We want the assume_ functions.
SF F N A SA
1 3 4 1 1

(Further discussion.)
We want the assume_ functions.
SF F N A SA
1 0 3 5 1

(Per discussion in P1188, we want a variation on the assume_ functions, and hope to forward that revision to LWG.)

[tituswinters]

We’re OK with the customization points.
strong_order, weak_order, etc are Neibloid customization points.
Unanimous consent

Rename the fallback functions, forward D0891R3 to LWG for C++20.
Unanimous consent

[jensmaurer]

Integrated into P1614 The Mothership Has Landed: Adding <=> to the Library #391.