Yul codegen for immutables.

test/libsolidity/semanticTests/immutable/assign_at_declaration.sol

@@ -4,5 +4,7 @@ contract A {
 		return a;
 	}
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 2

test/libsolidity/semanticTests/immutable/getter.sol

@@ -1,5 +1,7 @@
 contract C {
     uint immutable public x = 1;
 }
+// ====
+// compileViaYul: also
 // ----
 // x() -> 1

test/libsolidity/semanticTests/immutable/inheritance.sol

@@ -26,5 +26,7 @@ contract D is B, C {
 		return (a, b, c, d);
 	}
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 4, 3, 2, 1

test/libsolidity/semanticTests/immutable/internal_function_pointer.sol

@@ -10,6 +10,8 @@ contract C {
 		return z();
 	}
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 7
 // callZ() -> 7

test/libsolidity/semanticTests/immutable/stub.sol

@@ -9,5 +9,7 @@ contract C {
 		return (x+x,y);
 	}
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 84, 23

test/libsolidity/semanticTests/immutable/use_scratch.sol

@@ -13,6 +13,8 @@ contract C {
 		return (x+x,y);
 	}
 }
+// ====
+// compileViaYul: also
 // ----
 // constructor(): 3 ->
 // f() -> 84, 23