math.big: fix `a + b` and `a - b`, when the signs are different, add more test cases #7368

	name: Build Vinix

	on:
	workflow_call:
	pull_request:
	paths-ignore:
	- '**.md'
	- '**.yml'
	- '!**/vinix_ci.yml'
	- 'cmd/tools/vrepl.v'
	push:
	branches:
	- master
	paths-ignore:
	- '**.md'
	- '**.yml'
	- '!**/vinix_ci.yml'
	- 'cmd/tools/vrepl.v'

	concurrency:
	group: ${{ github.workflow }}-${{ github.ref == 'refs/heads/master' && github.sha \|\| github.ref }}
	cancel-in-progress: true

	jobs:
	vinix-build:
	runs-on: ubuntu-20.04
	timeout-minutes: 10
	steps:
	- uses: actions/checkout@v4
	- name: Build V
	run: make -j4 && ./v symlink

	- name: Install dependencies
	run: \|
	./v retry -- sudo apt update
	./v retry -- sudo apt install build-essential meson -y

	- name: Clone current Vinix
	run: ./v retry -- git clone https://github.com/vlang/vinix.git

	- name: Download Vinix kernel dependencies
	run: cd vinix/kernel && ./get-deps

	- name: Attempt to build the Vinix kernel (debug)
	run: cd vinix/kernel && make PROD=false KCFLAGS="-D__vinix__ -O2 -g -pipe" KV="../../v" && make clean

	- name: Attempt to build the Vinix kernel (prod)
	run: cd vinix/kernel && make PROD=true KCFLAGS="-D__vinix__ -O2 -g -pipe" KV="../../v" && make clean

	- name: Attempt to build the util-vinix (debug)
	run: cd vinix/util-vinix && make PROD=false V="$(realpath ../../v)" VFLAGS="-os vinix -gc none" KCFLAGS="-D__vinix__ -O2 -g -pipe" && make clean

	- name: Attempt to build the util-vinix (prod)
	run: cd vinix/util-vinix && make PROD=true V="$(realpath ../../v)" VFLAGS="-os vinix -gc none" KCFLAGS="-D__vinix__ -O2 -g -pipe" && make clean

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