CI: Add workflow to fail if autoconf/autoheader warnings are produced.

Author: notroj

.github/workflows/linux.yml

@@ -36,6 +36,11 @@ jobs:
               SKIP_TESTING=1
               TEST_LOGNO=1
           # -------------------------------------------------------------------------
+          - name: autoconf warnings test
+            env: |
+              BUILDCONFIG=--with-errors
+              SKIP_TESTING=1
+          # -------------------------------------------------------------------------
           - name: Default
           # -------------------------------------------------------------------------
           - name: All-static modules