Introduce tests which demonstrate bad wasm compiler.

substrate/wasm-runtime/support/src/lib.rs

@@ -144,7 +144,13 @@ macro_rules! impl_stubs {
 					};
 
 					let output = super::$name(&input[..]);
-					&output[0] as *const u8 as u64 + ((output.len() as u64) << 32)
+					// things break if we try to take the address of an unallocated vec, so we
+					// shortcircuit the empty output case.
+					if output.len() > 0 {
+						&output[0] as *const u8 as u64 + ((output.len() as u64) << 32)
+					} else {
+						0
+					}
 				}
 			)*
 		}