* ab/make-tags-cleanup:
Makefile: normalize clobbering & xargs for tags targets
Makefile: remove "cscope.out", not "cscope*" in cscope.out target
Makefile: don't use "FORCE" for tags targets
Makefile: add QUIET_GEN to "cscope" target
Makefile: move ".PHONY: cscope" near its target