Cross-architecture compilation & multilib Code coverage

One topic per page, each going deeper than the overview does.

Guide	Covers
Cross-architecture compilation & multilib	Targeting another architecture, and the host's secondary ABIs
Code coverage	The GNU and LLVM coverage tools, and which stage carries which

For the ways to run the images in the first place - dev container, CI, Compose, custom builds - see Using the images.
Start from the README to pick a stage.