Repository navigation

feat(xlings): provision `[xlings] deps` on first build, at global sco… #1469

Job	Run time
integration: mcpp builds & runs xlings	8m 32s
toolchain: musl + llvm	6m 7s
build + unit tests (linux x86_64, self-host)	13m 48s
toolchain: gcc (cold self-host)	8m 26s
	36m 53s