fix handling of end labels

- disallow using end label alone on blocks
- improved parse error for mismatches
- add label checking for non-block constructs
- allow generate block to have label before begin

test/basic/end_labels.sv

@@ -0,0 +1,45 @@
+class C #(
+    parameter X
+);
+    localparam Y = X * 2;
+endclass : C
+
+package P;
+    localparam Z = 3;
+endpackage : P
+
+`define DUMP(expr) initial $display(`"expr = %0d`", expr);
+
+interface intf;
+    initial $display("intf");
+endinterface : intf
+
+module top;
+    intf i();
+    function automatic integer f;
+        input integer inp;
+        return inp * 8;
+    endfunction : f
+    task t;
+        $display("t()");
+    endtask : t
+    localparam W = 4;
+    `DUMP(W)
+    `DUMP(C#(3)::X)
+    `DUMP(C#(3)::Y)
+    `DUMP(P::Z)
+    `DUMP(f(3))
+    initial t();
+    initial begin : blkA
+        $display("Hello!");
+    end : blkA
+    if (1) begin : blkB
+        initial $display("Bye!");
+    end : blkB
+    initial blkC : begin
+        $display("No!");
+    end : blkC
+    if (1) blkD : begin
+        initial $display("Way!");
+    end : blkD
+endmodule : top

test/basic/end_labels.v

@@ -0,0 +1,19 @@
+`define DUMP(expr, value) initial $display(`"expr = %0d`", value);
+
+module top;
+    `DUMP(W, 4)
+    `DUMP(C#(3)::X, 3)
+    `DUMP(C#(3)::Y, 6)
+    `DUMP(P::Z, 3)
+    `DUMP(f(3), 24)
+    if (1) initial begin
+        $display("intf");
+        $display("Bye!");
+        $display("Way!");
+    end
+    initial begin
+        $display("t()");
+        $display("Hello!");
+        $display("No!");
+    end
+endmodule