build: don't be too picky on make clean.
build: don't be too picky on make clean.

	* src/uobjects/local.mk: We have many "clean" that can be running
	in parallel, so be robust to "rm" be given files that no longer exist.

aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,aldebaran/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi,aldebaran/urbi,urbiforge/urbi,urbiforge/urbi