Fix some make distcheck failures

Fix some make distcheck failures

Apparently we forgot to add some test input files to the source
distribution.

Fixed thus.

	* tests/data/Makefile.am: Add
	test-diff-dwarf/test42-PR21296-libgcc.so,
	test-diff-dwarf/test42-PR21296-libclang.so,
	test-diff-dwarf/test42-PR21296-clanggcc-report0.txt to the source
	distribution.  Also look for test-diff-filter/test39* tests inputs
	in the test-diff-filter/test39/ directory.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>