Track skipped upstream commit IDs.

Track skipped upstream commit IDs.

There are a small number of "upstream" commits that do not correspond to
a file in -portable.  This file tracks those so that we can reconcile
OpenBSD and Portable to ensure that no commits are accidentally missed.

If you add something to .skipped-commit-ids please also add an upstream
ID line in the following format when you commit it.

    Upstream-ID: 321065a95a7ccebdd5fd08482a1e19afbf524e35
    Upstream-ID: d4f699a421504df35254cf1c6f1a7c304fb907ca
    Upstream-ID: aafe246655b53b52bc32c8a24002bc262f4230f7
    Upstream-ID: 8fa9cd1dee3c3339ae329cf20fb591db6d605120
    Upstream-ID: f31327a48dd4103333cc53315ec53fe65ed8a17a
    Upstream-ID: edbfde98c40007b7752a4ac106095e060c25c1ef
    Upstream-ID: 052fd565e3ff2d8cec3bc957d1788f50c827f8e2
    Upstream-ID: 7cf73737f357492776223da1c09179fa6ba74660
    Upstream-ID: 180d84674be1344e45a63990d60349988187c1ae
    Upstream-ID: f6ae971186ba68d066cd102e57d5b0b2c211a5ee