Proper error message for missing variables in inline assembly

test/libsolidity/syntaxTests/inlineAssembly/invalid/jump_invalid_label.sol

@@ -0,0 +1,10 @@
+contract C {
+  function f() public pure {
+    assembly {
+      jump(xy)
+    }
+  }
+}
+// ----
+// DeclarationError: (68-70): Identifier not found.
+// SyntaxError: (63-71): Jump instructions and labels are low-level EVM features that can lead to incorrect stack access. Because of that they are discouraged. Please consider using "switch", "if" or "for" statements instead.

test/libsolidity/syntaxTests/inlineAssembly/invalid/missing_variable.sol

@@ -0,0 +1,9 @@
+contract C {
+  function f() public pure {
+    assembly {
+      x := 1
+    }
+  }
+}
+// ----
+// DeclarationError: (63-64): Variable not found or variable not lvalue.