Add inlining for old optimizer.

test/cmdlineTests/optimizer_inliner_add/input.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity >=0.0;
+
+function unsafe_add(uint x, uint y) pure returns (uint)
+{
+    unchecked {
+        return x + y;
+    }
+}
+
+contract C {
+    function f() public pure {
+        for(uint x = 0; x < 10; x = unsafe_add(x, unsafe_add(x, 1)))
+        {
+        }
+    }
+}