Helix comes with support for clangd and clang-format out of the box! Refer to ClangdConfiguration for how to configure clangd.
To configure clangd command-line arguments, create a .helix/languages.toml file in the project root:
[language-server.serenity]
command = "clangd"
# clangd arguments, refer to ClangdConfiguration.md for what may be needed.
args = []
[[language]]
name = "cpp"
language-servers = ["serenity"]