Fix T54457: build error with OpenVDB versions newer than 3.

Solution provided by Sven-Hendrik Haase.

intern/openvdb/CMakeLists.txt

@@ -38,6 +38,7 @@ set(SRC
 if(WITH_OPENVDB)
 	add_definitions(
 		-DWITH_OPENVDB
+		-DOPENVDB_3_ABI_COMPATIBLE
 	)
 
 	list(APPEND INC_SYS

intern/openvdb/intern/openvdb_writer.cc

@@ -45,7 +45,7 @@ void OpenVDBWriter::insert(const openvdb::GridBase::Ptr &grid)
 
 void OpenVDBWriter::insert(const openvdb::GridBase &grid)
 {
-#if (OPENVDB_LIBRARY_MAJOR_VERSION_NUMBER == 3)
+#if (OPENVDB_LIBRARY_MAJOR_VERSION_NUMBER >= 3)
 	m_grids->push_back(grid.copyGrid());
 #else
 	m_grids->push_back(grid.copyGridWithNewTree());