graphics/embree: change default selection of the port's options (+)

OSPray, an allegedly important raytracing library, explicitly requires
Embree to be built with ISPC support and back-face culling disabled.

This might or might not affect other 3D applications and, particularly,
Blender, but could not reach Shane for his opinion in due time.

Requested by:	yuri
PR:		260031

graphics/embree/Makefile

@@ -2,6 +2,7 @@
 
 PORTNAME=	embree
 PORTVERSION=	3.13.2
+PORTREVISION=	1
 DISTVERSIONPREFIX=	v
 CATEGORIES=	graphics
 
@@ -19,15 +20,17 @@ USE_GITHUB=	yes
 
 CMAKE_ARGS=	-DEMBREE_TASKING_SYSTEM:STRING=${_ETS} \
 		-DCMAKE_INSTALL_DOCDIR:STRING=${DOCSDIR} \
-		-DEMBREE_BACKFACE_CULLING:BOOL=ON \
 		-DEMBREE_RAY_MASK:BOOL=ON
 
 PLIST_SUB+=	VERSION=${DISTVERSION}
 
-OPTIONS_DEFINE=	DOCS EXAMPLES ISPC TBB
-OPTIONS_DEFAULT=	TBB
+OPTIONS_DEFINE=	BACKFACE_CULLING DOCS EXAMPLES ISPC TBB
+OPTIONS_DEFAULT=	ISPC TBB
 OPTIONS_SUB=	yes
 
+BACKFACE_CULLING_DESC=	Enable back-face culling (BFC)
+BACKFACE_CULLING_CMAKE_ON=	-DEMBREE_BACKFACE_CULLING:BOOL=ON
+
 ISPC_DESC=		ISPC applications support
 ISPC_BUILD_DEPENDS=	ispc:devel/ispc
 ISPC_CMAKE_OFF=		-DEMBREE_ISPC_SUPPORT:BOOL=OFF