devel/ruby-ffi: update to 1.9.23

pkgsrc change: update HOMEPAGE

1.9.19 and 1.9.20 were not released.

1.9.21 2018/02/06

* Use PRIsVALUE shim when not available for Ruby < 2.0 compatibility.
* Drop Ruby 1.8.7 support (#480)
* Add support for Sparc64 Linux. (#574)
* Add support for MSYS2 (#572)
* Normalize sparc64 to sparcv9. (#575)
* Fix compatibility with PPC64LE platform (#577)
* Added support for Bitmask. (#573)
* Use Ruby implementation for `which` (#315)
* Do closures via libffi
* Do not assume a path to the sh and env binaries (#528)
* Fix typo of mprotect (#586)
* read_string should not throw an error on length 0
* optimise read_string for case if len is nil
* add missing win64 types fixes #588
* Upgrade to yard ~> 0.9 to silence Github dependency vulnerability warning.
* Use kramdown for markdown processing.
* update travis for latest ruby versions.
* Bump rake-compiler-dock dependency to add ruby-2.5 support (#599)
* Bump version again while I figure out how to build this thing.

1.9.22 2018/02/23

* Various fixes and more deterinistic gem packaging (#612)
* suppress unused variable warning
* Add Appveyor badge icon

* Fix failures on MacOS (#617)

1.9.23 -- 2018/02/25
* Fix repeated generation of autoconf files
* Update libffi to latest master
* Fix wrong path to search for configure
* README: Remove now unnecessary PaX workaround [ci skip]

(taca)