environment: Use os.path.basename() when checking mesonlib.meson_command
environment: Use os.path.basename() when checking mesonlib.meson_command

Without this, when one of Meson's parent directories contains
"python", unexpected option "-u" will be passed to Meson.

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