Our dblatex invocation uses several style components from the AsciiDoc
distribution, but those components are not available when building with
Asciidoctor. Move the command line arguments into a variable so it can
be overridden by the user or makefile configuration options.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>