[isoltest] Enforcing compileViaYul to be set if test can pass via yul

test/libsolidity/semanticTests/fallback/short_data_calls_fallback.sol

@@ -4,6 +4,8 @@ contract A {
     function fow() public { x = 3; }
     fallback () external { x = 2; }
 }
+// ====
+// compileViaYul: also
 // ----
 // (): hex"d88e0b"
 // x() -> 2