change build tools install dir

[webern]

Description

Currently, the location of buildsys and other binaries is fixed in the repo at tools/bin.
This will not work with out-of-tree builds where we need to use pre-built build tools.
Make it possible to install and call the build tools binaries from arbitrary locations.

Definition of Done

A PR is merged that allows the user to decide where buildsys and other build tools will be installed and called from.

id: br_toolsdir
Related to bottlerocket-os/bottlerocket#2669