mail/xmailbox: Fix build with llvm16

- Utilize OPTIONSNG

Sponsored by:	The FreeBSD Foundation

mail/xmailbox/Makefile

@@ -12,13 +12,21 @@ USE_XORG=	xaw
 
 OPTIONS_DEFINE=	DOCS
 
+.include <bsd.port.options.mk>
+
+.if ${OPSYS} == FreeBSD && ${OSVERSION} >= 1400091
+CFLAGS+=	-Wno-error=incompatible-function-pointer-types
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} -e "s|%%PREFIX%%|${PREFIX}|g" ${WRKSRC}/XMailbox.ad
 
 post-install:
 	@${MKDIR} ${STAGEDIR}${DATADIR}
 	${INSTALL_DATA} ${WRKSRC}/dingdong.au ${STAGEDIR}${DATADIR}
 	${INSTALL_DATA} ${WRKSRC}/ugotmail.au ${STAGEDIR}${DATADIR}
+
+post-install-DOCS-on:
 	@${MKDIR} ${STAGEDIR}${DOCSDIR}
 	${INSTALL_DATA} ${WRKSRC}/DISCLAIMER ${STAGEDIR}${DOCSDIR}
 	${INSTALL_DATA} ${WRKSRC}/README ${STAGEDIR}${DOCSDIR}