Merge pull request #11003 from ethereum/ir-bug-incorrect-return-variable-count

Fix IR bug on deleting storage variables of function type.

test/libsolidity/semanticTests/functionTypes/function_external_delete_storage.sol

@@ -0,0 +1,39 @@
+contract C {
+    function() external public x;
+    uint public y = 0;
+
+    function increment() public {
+        ++y;
+    }
+
+    function set() external {
+        x = this.increment;
+    }
+
+    function incrementIndirectly() public {
+        x();
+    }
+
+    function deleteFunction() public {
+        // used to lead to an ICE during IR
+        delete x;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// x() -> 0
+// y() -> 0
+// increment() ->
+// y() -> 1
+// set() ->
+// x() -> 0xfdd67305928fcac8d213d1e47bfa6165cd0b87bd09de08a0000000000000000
+// increment() ->
+// y() -> 2
+// incrementIndirectly() ->
+// y() -> 3
+// deleteFunction() ->
+// increment() ->
+// y() -> 4
+// incrementIndirectly() -> FAILURE
+// y() -> 4