Make AD warning be not an error so regression tests run

Author: hsutter

regression-tests/test-results/pure2-autodiff.cpp2.output

@@ -899,6 +899,7 @@ ad_test:/* @autodiff @print */ type =
         return;
     }
 }
+AD: Warning - reverse mode differentiation is very experimental
 
 
 ad_test_reverse:/* @autodiff<"reverse"> @print */ type = 
@@ -1439,6 +1440,5 @@ ad_test_2:/* @autodiff<"order=2"> @print */ type =
         return;
     }
 }
-
-pure2-autodiff.cpp2(195,1): error: while applying @autodiff - AD: Warning reverse mode differentiation is very experimental.
+ ok (all Cpp2, passes safety checks)
 

source/reflect.h

@@ -10196,7 +10196,7 @@ auto autodiff(meta::type_declaration& t) -> void
     }
 
     if (reverse) {
-        CPP2_UFCS(error)(t, "AD: Warning reverse mode differentiation is very experimental.");
+        std::cout << "AD: Warning - reverse mode differentiation is very experimental\n";
     }
 
     autodiff_context ad_ctx {order, reverse}; 

source/reflect.h2

@@ -6174,7 +6174,7 @@ autodiff: (inout t: meta::type_declaration) =
     }
 
     if reverse {
-        t.error("AD: Warning reverse mode differentiation is very experimental.");
+        std::cout << "AD: Warning - reverse mode differentiation is very experimental\n";
     }
 
     ad_ctx: autodiff_context = (order, reverse);