XFA: Suppress remaining failing corpus tests on Linux.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1417703011 .
diff --git a/testing/SUPPRESSIONS_linux b/testing/SUPPRESSIONS_linux
index 86e3a06..90fc0a2 100644
--- a/testing/SUPPRESSIONS_linux
+++ b/testing/SUPPRESSIONS_linux
@@ -1,3 +1,8 @@
 # List of tests to be skipped on linux platforms, one per line.
 # Try to keep the file alphabetized.
 format_custom_format.pdf
+# These XFA-only failures are in a separate section.
+050_extra_m.pdf
+3bigpreview.pdf
+example_033.pdf
+test_m.pdf