mcompile: Use the current dir if unspecified
mcompile: Use the current dir if unspecified

With this running `meson compile` inside the builddir actually works,
and you don't have to do `meson compile -C .`

Clearly this was the intent since the option already has `default='.'`

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