Use packages from nixpkgs where possible

[Atry]

I am working on porting our CMake build to Clang on Linux. It seems that we have some CMake files to build some bundled third-party libraries from source. However these CMake files are not compatible with Clang on Linux right now.

The reason we have those bundled third-party libraries is that these packages do not exist on the Ubuntu or Debian distributions that we are supporting. But since nixpkgs is a larger package registry than Ubuntu and Debian according to the statistics, we will have a larger chance to directly use packages from nixpkgs instead of building them from source. It would be an easy way to support Clang on Linux with Nix.

• fmt
• brotli
• Properly detect fmt #9223
• Use fmt_8 from nixpkgs instead of building it from source #9131