cpio: Disable gcc9 -Waddress-of-packed-member

cpio: Disable gcc9 -Waddress-of-packed-member

Disable the -Wadress-of-packaed-member diagnostic for the
grub_cpio_find_file function since the result is found to be false
postive. Any pointers to member of the 'struct head hd' is aligned even
if the structure is packed without paddings.

[   59s] In file included from ../grub-core/fs/cpio.c:51:
[   59s] ../grub-core/fs/cpio_common.c: In function 'grub_cpio_find_file':
[   59s] ../grub-core/fs/cpio_common.c:58:31: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    58 |   data->size = read_number (hd.filesize, ARRAY_SIZE (hd.filesize));
[   59s]       |                             ~~^~~~~~~~~
[   59s] ../grub-core/fs/cpio_common.c:60:29: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    60 |     *mtime = read_number (hd.mtime, ARRAY_SIZE (hd.mtime));
[   59s]       |                           ~~^~~~~~
[   59s] ../grub-core/fs/cpio_common.c:61:28: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    61 |   modeval = read_number (hd.mode, ARRAY_SIZE (hd.mode));
[   59s]       |                          ~~^~~~~
[   59s] ../grub-core/fs/cpio_common.c:62:29: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    62 |   namesize = read_number (hd.namesize, ARRAY_SIZE (hd.namesize));
[   59s]       |                           ~~^~~~~~~~~
[   59s] In file included from ../grub-core/fs/cpio_be.c:51:
[   59s] ../grub-core/fs/cpio_common.c: In function 'grub_cpio_find_file':
[   59s] ../grub-core/fs/cpio_common.c:58:31: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    58 |   data->size = read_number (hd.filesize, ARRAY_SIZE (hd.filesize));
[   59s]       |                             ~~^~~~~~~~~
[   59s] ../grub-core/fs/cpio_common.c:60:29: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    60 |     *mtime = read_number (hd.mtime, ARRAY_SIZE (hd.mtime));
[   59s]       |                           ~~^~~~~~
[   59s] ../grub-core/fs/cpio_common.c:61:28: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    61 |   modeval = read_number (hd.mode, ARRAY_SIZE (hd.mode));
[   59s]       |                          ~~^~~~~
[   59s] ../grub-core/fs/cpio_common.c:62:29: error: taking address of packed member of 'struct head' may result in an unaligned pointer value [-Werror=address-of-packed-member]
[   59s]    62 |   namesize = read_number (hd.namesize, ARRAY_SIZE (hd.namesize));
[   59s]       |                           ~~^~~~~~~~~

Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>