aacgain: build with -Wno-narrowing
aacgain: build with -Wno-narrowing

In recent GCC versions, -Wnarrowing is enabled by default, and compilation of
aacgain fails due to -Werror. This commit disables the warning again.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs