Merge pull request #12050 from ethereum/signedImmutablesBug

Fix signed immutables bug.

test/libsolidity/semanticTests/immutable/immutable_signed.sol

@@ -0,0 +1,15 @@
+contract C {
+    int8 immutable a = -2;
+    bytes2 immutable b = "ab";
+    function() internal returns (uint) immutable f = g;
+    function viaasm() view external returns (bytes32 x, bytes32 y) {
+        int8 _a = a;
+        bytes2 _b = b;
+        assembly { x := _a y := _b }
+    }
+    function g() internal pure returns (uint) { return 2; }
+}
+// ====
+// compileViaYul: also
+// ----
+// viaasm() -> 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffe, 0x6162000000000000000000000000000000000000000000000000000000000000

test/libsolidity/semanticTests/immutable/small_types_in_reverse.sol

@@ -0,0 +1,21 @@
+contract A {
+	uint16 public immutable a;
+	uint16 public immutable b;
+	uint16 public immutable c;
+	uint16[3] public x;
+	constructor() {
+		c = 0xffff;
+		b = 0x0f0f;
+		a = 0x1234;
+		x = [a, b, c];
+	}
+}
+// ====
+// compileViaYul: also
+// ----
+// a() -> 4660
+// b() -> 0x0f0f
+// c() -> 0xffff
+// x(uint256): 0 -> 4660
+// x(uint256): 1 -> 0x0f0f
+// x(uint256): 2 -> 0xffff