Incorrect artifact copy for some std libraries cause Merlin to fail to locate definitions

[voodoos]

A few modules of the Stdlib are copied from the otherlibs folder. Here are, for example, the rules for Unix:

flambda-backend/ocaml/otherlibs/unix/dune

Lines 44 to 62 in 4e08295

	(files
	(.unix.objs/native/unix.cmx as unix/unix.cmx)
	(.unix.objs/native/unixLabels.cmx as unix/unixLabels.cmx)
	(unix.cmxa as unix/unix.cmxa)
	(unix.a as unix/unix.a)
	(unix.cma as unix/unix.cma)
	(.unix.objs/byte/unix.cmi as unix/unix.cmi)
	(.unix.objs/byte/unix.cmti as unix/unix.cmti)
	(.unix.objs/byte/unixLabels.cmi as unix/unixLabels.cmi)
	(.unix.objs/byte/unixLabels.cmti as unix/unixLabels.cmti)
	(unix.cmxs as unix/unix.cmxs)
	(unix.mli as unix/unix.mli)
	(unixLabels.mli as unix/unixLabel.mli)
	(libunix_stubs.a as unix/libunix_stubs.a)
	(libunix_stubs.a as libunix_stubs_native.a) ; for special_dune compat
	(dllunix_stubs.so as stublibs/dllunix_stubs.so)
	(socketaddr.h as caml/socketaddr.h)
	(unixsupport.h as caml/unixsupport.h)
	)

There are a few things that prevent Merlin to find the information it needs:

• The cmt files are not copied, these are critical for Merlin functionality (jump-to-definition and document)
• There is at least one typo in (unixLabels.mli as unix/unixLabel.mli): it should be plural everywhere

Similar changes should also be made to the other libraries that are copied to the stdlib folder.

cc @ddickstein