Fix wrapper kind for C-like tagged enum

Fixes #126

src/bindgen/ir/enumeration.rs

@@ -353,7 +353,7 @@ impl Source for Enum {
             out.new_line();
 
             if config.language == Language::C {
-                out.write("typedef union");
+                write!(out, "typedef {}", if separate_tag { "struct" } else { "union" });
                 out.open_brace();
             }
 

tests/expectations/enum.c

@@ -83,7 +83,7 @@ typedef struct {
   int16_t y;
 } G_Bar_Body;
 
-typedef union {
+typedef struct {
   G_Tag tag;
   union {
     G_Foo_Body foo;
@@ -107,7 +107,7 @@ typedef struct {
   int16_t y;
 } H_Bar_Body;
 
-typedef union {
+typedef struct {
   H_Tag tag;
   union {
     H_Foo_Body foo;