"struct varlena" would be at least word-aligned.  Per buildfarm results
from gypsy_moth.  I did a little bit of trawling for other instances of
this coding pattern, and didn't find any; but if we turn up any more
of them I think we'd better revert the "char [4]" patch and find another
way of making tuptoaster.c alignment-safe.
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.127 2008/01/01 19:45:52 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.127.2.1 2008/03/01 19:26:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
    struct
    {
        bytea       hdr;
-       char        data[LOBLKSIZE];
+       char        data[LOBLKSIZE];    /* make struct big enough */
+       int32       align_it;   /* ensure struct is aligned well enough */
    }           workbuf;
    char       *workb = VARDATA(&workbuf.hdr);
    HeapTuple   newtup;
    struct
    {
        bytea       hdr;
-       char        data[LOBLKSIZE];
+       char        data[LOBLKSIZE];    /* make struct big enough */
+       int32       align_it;   /* ensure struct is aligned well enough */
    }           workbuf;
    char       *workb = VARDATA(&workbuf.hdr);
    HeapTuple   newtup;