Check for unrecognized *-sys dependencies

This adds another step to `pure-rust-build` that fails -- and fails
the job -- when there are any dependencies named `*-sys` other than
`linux-raw-sys`, which is known about.

(This is independent of the use of C in `ring` -- discussed
in #1681, #1682, and #1684 -- because `ring` is not, and does not
use, a `*-sys` dependency.)

This should fail prior to 3506afb (#1684) and pass afterwards.

Author: EliahKagan

.github/workflows/ci.yml

@@ -64,6 +64,9 @@ jobs:
           pattern='.*\b(-sys|cc|cmake|pkg-config|vcpkg)\b.*'
           ! GREP_COLORS='ms=30;48;5;214' grep --color=always -Ex -C 1000000 -e "$pattern" tree.txt
         continue-on-error: true
+      - name: Check for unrecognized *-sys dependencies
+        run: |
+          ! grep -qP '(?<!\blinux-raw)-sys\b' tree.txt
       - name: Wrap cc1 (and cc1plus if present) to record calls
         run: |
           cat >/usr/local/bin/wrapper1 <<'EOF'