devel/gwm: Update to 1.4.0

Move CARGO_CRATES to Makefile.crates: the list grew to 321 crates, which
buried the port's actual metadata under 300 lines of mechanical output.
Keeping it separate makes future updates a wholesale replacement of a
generated file (make cargo-crates > Makefile.crates) and leaves diffs to
the Makefile readable.