No-prelude example

This is an example project that does not rely on https://github.com/facebook/buck2-prelude. Instead the prelude cell points to a prelude directory with an empty prelude.bzl file, like so:

#.buckconfig
[cells]
root = .
prelude = prelude

All rules and toolchains are defined manually within each of the subdirectories. (e.g. cpp/rules.bzl, cpp/toolchain.bzl)

Sample commands

Install Buck2, cd into a project, and run

# List all targets
buck2 targets //...
# Build all targets
buck2 build //...
# Run C++ hello_world main
buck2 run //cpp/hello_world:main