ci: Test `make precomp`

ci/cirrus.sh

@@ -52,7 +52,19 @@ then
         $EXEC ./bench
     } >> bench.log 2>&1
 fi
+
 if [ "$CTIMETEST" = "yes" ]
 then
     ./libtool --mode=execute valgrind --error-exitcode=42 ./valgrind_ctime_test > valgrind_ctime_test.log 2>&1
 fi
+
+# Rebuild precomputed files (if not cross-compiling).
+if [ -z "$HOST" ]
+then
+    make clean-precomp
+    make precomp
+fi
+
+# Check that no repo files have been modified by the build.
+# (This fails for example if the precomp files need to be updated in the repo.)
+git diff --exit-code