Log Message:
SDL2: Fix pkg-config .pc file and fix pulseaudio option

* Bump PKGREVISION.
* sdl2.pc has -liconv in Libs.private and it is incorrect.
  Detect iconv function in libc.
* Fix pulseaudio option by disabling shared link.
* Add pulseaudio support to buildlink3.mk to fix fonts/SDL2_ttf
  when pulseaudio option is enable in devel/SDL2.