testsuite: Fix up pr103456.c testcase [PR103456]

testsuite: Fix up pr103456.c testcase [PR103456]

ubsan.exp cycles through torture options, and that includes
-O2 -flto -fno-fat-lto-objects.  But with those options
tree dump scans don't work for post-IPA passes, for dg-do
compile tests nothing after IPA is done.  So we get an
unresolved testcase:
gcc.dg/ubsan/pr103456.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  : dump file does not exist
UNRESOLVED: gcc.dg/ubsan/pr103456.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects   scan-tree-dump-not objsz1 "maximum object size 0"

Fixed by adding -ffat-lto-objects so that we perform the post-IPA
passes.

2021-12-03  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/103456
	* gcc.dg/ubsan/pr103456.c: Add -ffat-lto-objects to dg-options.