configure: undefine USE_MYSQL on configuration failure #508

	---
	name: GCC C/C++ standards check

	on:
	- push

	jobs:
	build:
	name: ${{ matrix.c }} & ${{ matrix.cpp }}

	concurrency:
	group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.head_ref \|\| github.sha }}-${{
	matrix.c }}-${{ matrix.cpp }}
	cancel-in-progress: true

	runs-on: ubuntu-22.04
	strategy:
	matrix:
	include:
	- c: gnu11
	cpp: c++11
	fail-fast: false

	steps:
	- uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4
	- name: Get dependencies
	run: \|
	sudo apt-get update -y
	sudo apt-get install -y wget git gawk findutils
	xargs -a <(awk '! /^ *(#\|$)/' ".github/workflows/apt.txt") -r -- \
	sudo apt-get install -y --no-install-recommends --no-install-suggests
	- name: Create installation directory
	run: \|
	mkdir $HOME/install
	- name: Ensure one core for compilation
	run: \|
	echo "MAKEFLAGS=-j1" >> $GITHUB_ENV
	- name: Set LD_LIBRARY_PATH for compilation
	run: \|
	echo "LD_LIBRARY_PATH=$HOME/install/lib" >> $GITHUB_ENV
	- name: Print build environment variables
	shell: bash -el {0}
	run: \|
	printenv \| sort
	gcc --version
	ldd --version
	- name: Build
	env:
	# TODO: -pedantic-errors here won't go through ./configure (with GNU C)
	CFLAGS: -std=${{ matrix.c }} -fPIC -Wall -Wextra
	# TODO: -pedantic-errors here won't compile
	CXXFLAGS: -std=${{ matrix.cpp }} -fPIC -Wall -Wextra
	run: \|
	.github/workflows/build_ubuntu-22.04.sh $HOME/install \
	-isystem/usr/include/gdal -Wpedantic -Werror

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