GNUmakefile includes maint.mk but does not depend on maintainer-makefile

[Ralf Wildenhues]

Hello all,

maintainer-makefile depends on gnumakefile, but not vice versa, yet
top/GNUmakefile (which is part of the latter module) includes maint.mk
(which is part of the former) unconditionally.

Either gnumakefile should also depend on maintainer-makefile (which
means both modules could be merged), or for example 'sinclude' aka
'-include' should be used to include maint.mk, or at least the
gnumakefile module description should mention that one has to write
a maint.mk file.

Reproduce with
  gnulib-tool --with-tests --test gnumakefile

What do you think?

Thanks,
Ralf