adding a test that checks for attribute contracts with fcontracts-nonattr

Author: NinaRanns

gcc/testsuite/g++.dg/contracts/cpp26-attr/check-err.C

@@ -0,0 +1,15 @@
+// test that attribute syntax is diagnosed when using -fcontracts-nonattr
+// { dg-do compile }
+// { dg-options "-std=c++2a -fcontracts -fcontracts-nonattr" }
+
+int fun(int n)  [[ pre : n > 0 ]]; // { dg-error "contracts are not available with" }
+int fun2(const int n)  [[ post : n > 0 ]]; // { dg-error "contracts are not available with" }
+
+int main()
+{
+  int x;
+
+  [[assert: x >= 0]]; // { dg-error "ontracts are not available with" }
+
+  return 0;
+}