[config] Suppress implicit-fallthrough

Change-Id: Ief5fd9bb3a27b2be3a3b01a1ccbb96426623a5f5
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/wayland/+/527270
Reviewed-by: Shai Barack <shayba@google.com>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 5deaa31..7bd4750 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -77,7 +77,6 @@
 config("common_config") {
   visibility = [ ":*" ]
   include_dirs = [ "${target_gen_dir}/common" ]
-  cflags = [ "-Wno-conversion" ]
 }
 
 config("client_config") {
@@ -113,6 +112,9 @@
       # element, a warning is raised.
       "-Wno-unknown-warning-option",
       "-Wno-sizeof-array-div",
+
+      "-Wno-conversion",
+      "-Wno-implicit-fallthrough",
     ]
   }
 }