meson: Run ninja under devenv
Unlike libtool, meson doesn't set the LD_LIBRARY_PATH environment variable for running uninstalled executables by default. If the build process requires running uninstalled executables, it may fail because LD_LIBRARY_PATH set by JHBuild may instruct it to prefer the installed library to the uninstalled one. To fix it, use the 'devenv' subcommand introduced in Meson 0.58 to setup the environment for ninja.
https://github.com/mesonbuild/meson/issues/1635 https://github.com/mesonbuild/meson/pull/8393