[clang] [analyzer] Ignore [[clang::flag_enum]] enums in the EnumCastOutOfRange checker (PR #141232)

[Balazs Benics via cfe-commits]

steakhal wrote:

> Should we still warn if we store a negative value or a value >= 2*last member?

I was thinking about this but I chose the simplest way to suppress these.

https://github.com/llvm/llvm-project/pull/141232