Merge branch 'jc/make-dedup-ls-files-output'

Merge branch 'jc/make-dedup-ls-files-output'

A "ls-files" that emulates "find" to enumerate files in the working
tree resulted in duplicated Makefile rules that caused the build to
issue an unnecessary warning during a trial build after merge
conflicts are resolved in working tree *.h files but before the
resolved results are added to the index.  This has been corrected.

* jc/make-dedup-ls-files-output:
  Makefile: dedup list of files obtained from ls-files