Test with gcc 8 and fix a few minor warnings and issues
diff --git a/src/qcbor_decode.c b/src/qcbor_decode.c
index 2c301b6..8d216c7 100644
--- a/src/qcbor_decode.c
+++ b/src/qcbor_decode.c
@@ -536,6 +536,7 @@
             nReturn = QCBOR_ERR_INVALID_CBOR;
             goto Done;
          }
+         /* FALLTHROUGH */
          // fall through intentionally
 
       default: // 0-19