testsuite: Silence analyzer/pr51628-30.c for default_packed

testsuite: Silence analyzer/pr51628-30.c for default_packed

On default_packed targets like PRU, a warning in the file included from
analyzer/pr51628-30.c is reported as spurious one, even though it has been
annotated there:

  Excess errors:
  gcc/gcc/testsuite/gcc.dg/analyzer/torture/../../../c-c++-common/pr51628-30.c:7:19: warning: 'packed' attribute ignored for field of type 'struct B' [-Wattributes]

Mark that gcc.dg/analyzer/torture/pr51628-30.c generates excess warnings
for default_packed targets.  This is safe because the original test case
covered an ICE, not a diagnostic error.

gcc/testsuite/ChangeLog:

	* gcc.dg/analyzer/torture/pr51628-30.c: Test can spill excess
	errors for default_packed targets.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>