textproc/hs-pandoc: Switch to static build and fix option issues

• With the default options, there were many large dependencies, including ghc. Most users likely just want the application without the compiler and libraries, so switch to a static build.
• The build was failing with a few non-default option combinations (e.g, with HTTPS off). Fix these and/or remove options that are probably not that useful for most users.
• The binary is linked to libffi.so, so add LIB_DEPENDS on devel/libffi.
• Pacify portlint

Reported by: adamw
Approved by: maintainer (haskell via arrowd)
Differential Revision: https://reviews.freebsd.org/D18899