[Wconversion] Fix implicit conversion issue

Make a cast from long to int explicit.

Bug: 58162
Change-Id: I84aa84e59f50b6e87bec56bacd2f0a587d53a949
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/wayland/+/430718
Reviewed-by: Petr Hosek <phosek@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a0eaf66..5deaa31 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -77,6 +77,7 @@
 config("common_config") {
   visibility = [ ":*" ]
   include_dirs = [ "${target_gen_dir}/common" ]
+  cflags = [ "-Wno-conversion" ]
 }
 
 config("client_config") {
@@ -112,7 +113,6 @@
       # element, a warning is raised.
       "-Wno-unknown-warning-option",
       "-Wno-sizeof-array-div",
-      "-Wno-conversion",
     ]
   }
 }