mconf: Report all unknown cmd line options instead of aborting on first
mconf: Report all unknown cmd line options instead of aborting on first

This is also more consistent with the error message returned by
optinterpreter when it finds unknown command line options.

thiblahute/meson,becm/meson,MathieuDuponchelle/meson,MathieuDuponchelle/meson,QuLogic/meson,jpakkane/meson,thiblahute/meson,pexip/meson,jpakkane/meson,becm/meson,becm/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,thiblahute/meson,QuLogic/meson,MathieuDuponchelle/meson,pexip/meson,pexip/meson,becm/meson,jeandet/meson,becm/meson,pexip/meson,QuLogic/meson,jpakkane/meson,thiblahute/meson,pexip/meson,jeandet/meson,QuLogic/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,MathieuDuponchelle/meson,jpakkane/meson,mesonbuild/meson,thiblahute/meson,MathieuDuponchelle/meson,jpakkane/meson,mesonbuild/meson,jeandet/meson,jeandet/meson,becm/meson,jeandet/meson,mesonbuild/meson,jeandet/meson,thiblahute/meson,MathieuDuponchelle/meson,jeandet/meson,jpakkane/meson,pexip/meson,becm/meson,becm/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,MathieuDuponchelle/meson,jpakkane/meson,QuLogic/meson,jeandet/meson,thiblahute/meson,thiblahute/meson,QuLogic/meson,MathieuDuponchelle/meson,becm/meson,jeandet/meson,MathieuDuponchelle/meson,mesonbuild/meson,QuLogic/meson,QuLogic/meson,jpakkane/meson,jpakkane/meson,becm/meson,QuLogic/meson,thiblahute/meson,pexip/meson