Suppress -Wimplicit-fallthrough.

-Wimplicit-fallthrough will be enabled globally.

Test: build with global -Wimplicit-fallthrough.
Change-Id: Ie77da5d795217624b7b174985409a6e8c8b72e53
diff --git a/Android.bp b/Android.bp
index d11b36e..ab7a598 100644
--- a/Android.bp
+++ b/Android.bp
@@ -13,6 +13,9 @@
         "-Wno-unused-parameter",
         "-Wno-sign-compare",
         "-Wno-missing-field-initializers",
+        "-Wno-implicit-fallthrough",
+        // cpdf_renderstatus.cpp:1768, cpdf_variabletext.cpp:320,
+        // and cpwl_edit_impl.cpp:1825 have -Wimplicit-fallthrough.
         "-Werror",
 
         "-DOPJ_STATIC",