Create option target helpers.

[mat]

Summary

It will permit replacing:

  .include <bsd.port.options.mk>
  
  post-patch:
	  ${REINPLACE_CMD} -e 's|/usr/local|${LOCALBASE}|g' \
		  ${WRKSRC}/Configure ${WRKSRC}/hints/freebsd.sh
  .if ${PORT_OPTIONS:MPTHREAD}
	  ${REINPLACE_CMD} -e 's|%%PTHREAD_LIBS%%|-lpthread|g;' \
		  ${WRKSRC}/hints/freebsd.sh
  .else
	  ${REINPLACE_CMD} -e 's|%%PTHREAD_LIBS%%||g;' \
		  ${WRKSRC}/hints/freebsd.sh
  .endif

with:

  post-patch:
	  ${REINPLACE_CMD} -e 's|/usr/local|${LOCALBASE}|g' \
		  ${WRKSRC}/Configure ${WRKSRC}/hints/freebsd.sh
  post-patch-PTHREAD-on:
	  ${REINPLACE_CMD} -e 's|%%PTHREAD_LIBS%%|-lpthread|g;' \
		  ${WRKSRC}/hints/freebsd.sh
  post-patch-PTHREAD-off:
	  ${REINPLACE_CMD} -e 's|%%PTHREAD_LIBS%%||g;' \
		  ${WRKSRC}/hints/freebsd.sh

so that there's even less need to .include bsd.port.options.mk.

[mat]

Looks like pre-stage-*-o{n,ff} were forgotten there. Also there is no pre-stage target.