Only warn about variables being shadowed in inline assembly.

test/libsolidity/semanticTests/inlineAssembly/shadowing_local_function_opcode.sol

@@ -0,0 +1,13 @@
+contract C {
+    function add(uint, uint) public pure returns (uint) { return 7; }
+    function g() public pure returns (uint x, uint y) {
+        x = add(1, 2);
+        assembly {
+            y := add(1, 2)
+        }
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// g() -> 7, 3