README.md: add build status #4

	name: Musl
	on:
	push:
	branches:
	- main
	tags: ['*']
	pull_request:
	workflow_dispatch:

	concurrency:
	# Skip intermediate builds: always.
	# Cancel intermediate builds: only if it is a pull request build.
	group: ${{ github.workflow }}-${{ github.ref }}
	cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}

	jobs:
	test:
	name: alpine
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v1
	- name: Set up Alpine Linux
	uses: jirutka/setup-alpine@v1
	with:
	arch: x86_64
	branch: latest-stable
	packages: >
	build-base
	- name: Env Version
	run: \|
	gcc --version
	ld --version
	apk info musl
	shell: alpine.sh {0}
	- name: Run Test
	run: make -j`nproc`
	shell: alpine.sh {0}
	- name: Show Test Result
	run: cat src/REPORT

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