Setting makeinfo options

----------------------------------------------------------------

I have been making a makefile to generate my package documentation,
with ideas from the emacs documentation makefile.

How would one allow users to decide what options to use - for html
for example?  Using variable hopc by appending makeinfo options=20
seems difficult, possibly wrong.


.PHONY: all-doc info html pdf dvi ps
--all-doc: info html pdf dvi ps

## [Syntax] targets: prerequisites
info: ${infdir}/antares.info
html: ${hmldir}/antares.html
pdf: ${docdir}/antares.pdf
dvi: ${docdir}/antares.dvi
ps: ${docdir}/antares.ps


hopc :=3D

ifneq ($(strip $(css)),)
=09hopc +=3D --css-include=3D$(css)
endif

ifneq ($(strip $(css-ref)),)
=09hopc +=3D --css-ref=3D$(css-ref)
endif

ifneq ($(strip $(links)),)
=09hopc +=3D --internal-links=3D$(links)
endif

ifneq ($(strip $(split)),)
=09hopc +=3D --split=3D$(split)
endif

ifneq ($(trlfn),)
=09hopc +=3D --transliterate-file-names
endif

ifneq ($(ndf),)
=09hopc +=3D --node-files
endif

.PHONY: trlfn ndf

trlfn:
=09hopc +=3D --transliterate-file-names

ndf:
=09hopc +=3D --node-files

.PHONY: split-chapter split-section split-node

split-chapter:
=09split=3D--split=3Dchapter

split-section:
=09split=3D--split=3Dsection

split-node:
=09split=3D--split=3Dnode

split-chapter split-section split-node: $(hmldir)/antares.html

$(hmldir)/antares.html: $(srcs) | $$(@D)
=09makeinfo $(opts) --html $(hopc) -o $@ $<