test: commit a verify-build failure-mode battery and run it from make check (closes #227)

script/check

@@ -1,12 +1,13 @@
 #!/bin/sh
-# script/check: run all checks (test, lint, fmt-check). Our own
-# extension to scripts-to-rule-them-all. Must not modify any files.
+# script/check: run all checks (test, test-verify-build, lint, fmt-check).
+# Our own extension to scripts-to-rule-them-all. Must not modify any files.
 set -eu
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd -P)"
 
 main() {
     "$SCRIPT_DIR/test"
+    "$SCRIPT_DIR/test-verify-build"
     "$SCRIPT_DIR/lint"
     "$SCRIPT_DIR/fmt-check"
 }