Updating portage cache
These options tell you what packages would be installed if you were installing from scratch and you didn't have any of its dependencies yet.
The --verbose option will also show the set of USE flags that can be turned on and off for the packages to hopefully trim dependencies: For an accurate estimate, the above requires manually excluding files that would normally be removed due to the INSTALL_MASK (defined in src/scripts/common.sh).
For the host, the root directory where things get installed is /, for a given target board this is /build/.
Notice that since we are updating the host, we use the standard emerge command that installs packages at the root and uses the host's configuration: We set up a new sysroot per target board that we want to cross compile for.The board overlay can also include a that overrides some of our defaults such as compiler CFLAGS.When cross-compiling, you also need packages that correspond to the target, such as header files and libraries.In order to cross-compile, you need some tools that are run on the host in order to build individual packages.When we set up the system, we install the package to cover these.