Merge branch 'js/find-lib-h-with-ls-files-when-possible'

Merge branch 'js/find-lib-h-with-ls-files-when-possible'

The Makefile uses 'find' utility to enumerate all the *.h header
files, which is expensive on platforms with slow filesystems; it
now optionally uses "ls-files" if working within a repository,
which is a trick similar to how all sources are enumerated to run
ETAGS on.

* js/find-lib-h-with-ls-files-when-possible:
  Makefile: use `git ls-files` to list header files, if possible