Ignore -Wcast-qual warning

Clang 6.0.1 update introduced a number of new warnings, failing
werror build. Ignore the -Wcast-qual warning for external/wayland.

Test: m checkbuild
Change-Id: If16b9c46cf477e2db96b052f7f4412004ad1d407
diff --git a/Android.bp b/Android.bp
index 37da003..24df14d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -18,12 +18,13 @@
     cflags: [
         "-Wall",
         "-Wextra",
-        "-Wno-unused-parameter",
         "-g",
         "-Wstrict-prototypes",
         "-Wmissing-prototypes",
         "-fvisibility=hidden",
+        "-Wno-cast-qual",
         "-Wno-pointer-arith",
+        "-Wno-unused-parameter",
     ],
 }