typelib: Fix invalid alignment assumptions

The current source has invalid assumptions about structure alignment
that break on platforms like m68k where 32-bit integers are aligned to
16-bit only. Fix this by introducing explicit structure padding for
32-bit quantities following odd numbers of 16-bit quantities and
structure trail padding, to make the binary representation generated
by the compiler match the text of the specification exactly.

https://bugzilla.gnome.org/show_bug.cgi?id=661839

gitypelib-internal.h

@@ -282,7 +282,7 @@ typedef struct {
   guint32 sections;
 
   /* <private> */
-  guint16 padding[5];
+  guint16 padding[6];
 } Header;
 
 typedef enum {
@@ -434,6 +434,10 @@ typedef struct {
   gint8        closure;
   gint8        destroy;
 
+  /* <private> */
+  guint16      padding;
+  /* <public> */
+
   SimpleTypeBlob arg_type;
 } ArgBlob;
 
@@ -1051,6 +1055,8 @@ typedef struct {
   guint16 n_vfuncs;
   guint16 n_constants;
 
+  guint16 padding;
+
   guint32 reserved2;
   guint32 reserved3;