Meson find_program not finding program - mysql

Question

I'm building a Vala program with gnome-builder and flatpak. I wan't to connect to a mySQL Database. Thats why I need to run mysql_config to get the right compiler flags.
So I added mysql_config = find_program('mysql_config')to my meson.build file.
When I try to compile I get meson.build:7:0: ERROR: Program(s) ['mysql_config'] not found or not executable.
When I run whereis mysql_config on command line I get the expected result mysql_config: /usr/bin/mysql_config. Also I can run mysql_config --cflags from command line with the expected result -I/usr/include/mysql -I/usr/include/mysql.
Thats why I think that the problem is that I'm building with flatpak-builder.
My ./meson.build:
project('zeiterfassunggtk', ['c', 'vala'], version: '0.1.0',
meson_version: '>= 0.40.0',
)
i18n = import('i18n')
mysql_config = find_program('mysql_config')
mysql_vapi = meson.get_compiler('vala').find_library('mysql')
mysql_dep = declare_dependency(c_args: run_command([mysql_config, '--cflags']).stdout().split(),
link_args: run_command([mysql_config, '--libs']).stdout().split(),
dependencies: [mysql_vapi])
subdir('data')
subdir('src')
subdir('po')
meson.add_install_script('build-aux/meson/postinstall.py')
My ./src/meson.build
zeiterfassunggtk_sources = [
'main.vala',
'window.vala',
'mysql.vala',
]
zeiterfassunggtk_deps = [
dependency('gio-2.0', version: '>= 2.50'),
dependency('gtk+-3.0', version: '>= 3.22'),
]
gnome = import('gnome')
zeiterfassunggtk_sources += gnome.compile_resources('zeiterfassunggtk-resources',
'zeiterfassunggtk.gresource.xml',
c_name: 'zeiterfassunggtk'
)
executable('zeiterfassunggtk', zeiterfassunggtk_sources,
vala_args: '--target-glib=2.50', dependencies: zeiterfassunggtk_deps,
install: true,
)
The full output of the build process:
flatpak build --env=LANG=de_AT.UTF-8 --env=USER=g.zehetner --env=HOME=/home/g.zehetner --env=PATH=/usr/bin:/bin --env=TERM=xterm-256color --env=V=0 --env=CCACHE_DIR=/home/g.zehetner/.cache/gnome-builder/flatpak-builder/ccache --env=PATH=/app/bin:/usr/bin --build-dir=/home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/builds/org.gnome.Zeiterfassunggtk.json-flatpak-org.gnome.Platform-x86_64-3.26-master --share=network --nofilesystem=host --filesystem=/home/g.zehetner/.cache/gnome-builder --filesystem=/home/g.zehetner/Projekte/ZeiterfassungGtk --filesystem=/home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/builds/org.gnome.Zeiterfassunggtk.json-flatpak-org.gnome.Platform-x86_64-3.26-master --env=V=1 '--env=CFLAGS=-O2 -g' '--env=CXXFLAGS=-O2 -g' --env=NOCONFIGURE=1 /home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/flatpak/staging/x86_64-master ninja
[0/1] Regenerating build files.
The Meson build system
Version: 0.46.0
Source dir: /home/g.zehetner/Projekte/ZeiterfassungGtk
Build dir: /home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/builds/org.gnome.Zeiterfassunggtk.json-flatpak-org.gnome.Platform-x86_64-3.26-master
Build type: native build
Project name: zeiterfassunggtk
Native C compiler: ccache cc (gcc 6.2.0 "cc (GCC) 6.2.0")
Appending CFLAGS from environment: '-O2 -g'
Appending LDFLAGS from environment: '-L/app/lib '
Native Vala compiler: valac (valac 0.38.2)
Appending LDFLAGS from environment: '-L/app/lib '
Build machine cpu family: x86_64
Build machine cpu: x86_64
Program mysql_config found: NO
meson.build:7:0: ERROR: Program(s) ['mysql_config'] not found or not executable
A full log can be found at /home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/builds/org.gnome.Zeiterfassunggtk.json-flatpak-org.gnome.Platform-x86_64-3.26-master/meson-logs/meson-log.txt
FAILED: build.ninja
/usr/bin/python3 /usr/bin/meson --internal regenerate /home/g.zehetner/Projekte/ZeiterfassungGtk /home/g.zehetner/.cache/gnome-builder/projects/ZeiterfassungGtk/builds/org.gnome.Zeiterfassunggtk.json-flatpak-org.gnome.Platform-x86_64-3.26-master --backend ninja
ninja: error: rebuilding 'build.ninja': subcommand failed
You can find the full code at Github.com