Improve cross-compilation argument

[rota1001]

Previously, the arguments for cross-compilation were not intuitive, requiring users to read the build script to figure them out.

For example, the aarch target has to be built with the following commands, which is exhausting:

$ scripts/fetch-lkl.sh aarch64
$ make LKL_DIR=`pwd`/lkl-aarch64 CC=aarch64-linux-gnu-gcc BUILD=release
$ make ALPINE_ARCH=aarch64 rootfs

This changes it to a simple ARCH argument, and the same thing can be done by the following commands:

$ make ARCH=aarch64 CC=aarch64-linux-gnu-gcc
$ make ARCH=aarch64 CC=aarch64-linux-gnu-gcc rootfs

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Summary by cubic

Simplified cross-compilation by adding a single ARCH make variable that defaults to uname -m and flows through build, LKL fetch, and rootfs. Building targets like aarch64 is now a one-liner; host builds are unchanged.

• New Features
  • Plumbed ARCH into LKL_DIR, fetch-lkl.sh (including the fetch-lkl target), and ALPINE_ARCH for mkrootfs.sh.
  • Updated README.md with ARCH/CC examples and Quick Start notes for host vs target rootfs.

^{Written for commit 535544f. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="README.md">

<violation number="1" location="README.md:89">
P2: Cross-compilation example omits `BUILD=release`, but default debug build enables ASAN/UBSAN, which can break cross-linking when target sanitizer runtimes are unavailable.</violation>
</file>

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[jserv]

Rebase latest 'main' branch to resolve CI breakage.

[jserv]

Thank @rota1001 for contributing!