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

test/libsolidity/semanticTests/reverts/invalid_enum_as_external_arg.sol

@@ -15,6 +15,7 @@ contract C {
         return this.tested(garbled);
     }
 }
-
+// ====
+// compileViaYul: also
 // ----
 // test() -> FAILURE # should throw #

test/libsolidity/semanticTests/reverts/revert.sol

@@ -14,6 +14,8 @@ contract C {
     }
 }
 
+// ====
+// compileViaYul: also
 // ----
 // f() -> FAILURE
 // a() -> 42

test/libsolidity/semanticTests/reverts/simple_throw.sol

@@ -6,6 +6,8 @@ contract Test {
     }
 }
 
+// ====
+// compileViaYul: also
 // ----
 // f(uint256): 11 -> 21
 // f(uint256): 1 -> FAILURE