Add support for LLVM 18 (and use it by default) #130

	# Test whether we can link to LLVM installed from apt.llvm.org or Homebrew.
	---

	name: Test

	on: [push, pull_request]

	jobs:
	test-macos:
	runs-on: macos-latest
	strategy:
	matrix:
	llvm: [14, 15, 16, 17, 18]
	steps:
	- name: Checkout
	uses: actions/checkout@v4
	- name: Set up Go
	uses: actions/setup-go@v5
	with:
	go-version: '1.22'
	#- name: Update Homebrew
	# if: matrix.llvm == 17 # needed as long as LLVM 17 is still fresh
	# run: brew update
	- name: Install LLVM
	run: HOMEBREW_NO_AUTO_UPDATE=1 brew install llvm@${{ matrix.llvm }}
	- name: Test LLVM ${{ matrix.llvm }}
	run:
	go test -v -tags=llvm${{ matrix.llvm }}
	- name: Test default LLVM
	if: matrix.llvm == 18
	run:
	go test -v
	test-linux:
	runs-on: ubuntu-20.04
	strategy:
	matrix:
	llvm: [14, 15, 16, 17, 18]
	steps:
	- name: Checkout
	uses: actions/checkout@v4
	- name: Set up Go
	uses: actions/setup-go@v5
	with:
	go-version: '1.22'
	- name: Install LLVM
	run: \|
	echo 'deb http://apt.llvm.org/focal/ llvm-toolchain-focal-${{ matrix.llvm }} main' \| sudo tee /etc/apt/sources.list.d/llvm.list
	wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key \| sudo apt-key add -
	sudo apt-get update
	sudo apt-get install --no-install-recommends llvm-${{ matrix.llvm }}-dev
	- name: Test LLVM ${{ matrix.llvm }}
	run:
	go test -v -tags=llvm${{ matrix.llvm }}
	- name: Test default LLVM
	if: matrix.llvm == 18
	run:
	go test -v

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