add -Wno-deprecated-copy to fuchsia builds (#456)
add -Wno-deprecated-copy to fuchsia builds (#456)

https://github.com/flutter/flutter/issues/83268

Fuchsia is failing to build because the new flexible enums are
tripping up the deprecated-copy warning (fxbug.dev/77383.) This
removes the warning for fuchsia builds to roll the new clang.
flutter/buildroot,flutter/buildroot,flutter/buildroot,flutter/buildroot