Attempt to improve application portability by marking `struct ar_hdr'

Attempt to improve application portability by marking `struct ar_hdr'
as `packed'.

The C standard leaves the alignment of individual members of a C
struct upto the implementation, so pedantically speaking portable
code cannot assume that the layout of a `struct ar_hdr' in memory
will match its layout in a file.  Using a __packed attribute
declaration forces file and memory layouts for this structure to
match.

Submitted by:	ru