testsuite: Fix up pr98099.c testcase for big endian [PR98099]

testsuite: Fix up pr98099.c testcase for big endian [PR98099]

The testcase fails on big-endian without int128 support, because
due to -fsso-struct=big-endian no swapping is needed for big endian.
This patch restricts the testcase to big or little endian (but not pdp)
and uses -fsso-struct=little-endian for big endian, so that it is
swapping everywhere.

2021-03-18  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/98099
	* gcc.dg/pr98099.c: Don't compile the test on pdp endian.
	For big endian use -fsso-struct=little-endian dg-options.