testsuite: Handle "packed" targets in c-c++-common/auto-init-7.c and -8.c

testsuite: Handle "packed" targets in c-c++-common/auto-init-7.c and -8.c

Looks like there's a failed assumption that
sizeof (union U { char u1[5]; int u2; float u3; }) == 8.
However, for "packed" targets like cris-elf, it's 5.

These two tests have always failed for cris-elf.  I see from
https://gcc.gnu.org/pipermail/gcc-testresults/2023-February/777912.html
that they fail on pru-elf too, but I don't know if the cause
(and/or remedy) is the same.

IMHO this is preferred over the alternative; splitting up
that last line into two lines, like:
/* { dg-final { scan-tree-dump "temp4 = \
 .DEFERRED_INIT \\(8, 2, \&\"temp4\"" "gimple" { target { ! default_packed } } } } */
/* { dg-final { scan-tree-dump "temp4 = \
 .DEFERRED_INIT \\(5, 2, \&\"temp4\"" "gimple" { target default_packed } } } */

gcc/testsuite:
	* c-c++-common/auto-init-7.c, c-c++-common/auto-init-8.c: Also
	match targets where sizeof (union U) == 5, like "packed" targets.