Regardless of whether or not the dir is renamed to bfs, here is a Jamfile. It doesn't compile on my machine, but I remember having heard something about a Be header file missing a declaration.

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@55 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/add-ons/kernel/file_systems/befs/Jamfile

@@ -1,2 +1,17 @@
 SubDir OBOS_TOP src add-ons kernel file_systems befs ;
 
+Addon obfs : [ FDirName kernel file_systems befs ] :
+	BlockAllocator.cpp
+	BPlusTree.cpp
+	cpp.cpp
+	Debug.cpp
+	Index.cpp
+	Inode.cpp
+	Journal.cpp
+	kernel_interface.cpp
+	Query.cpp
+	Utility.cpp
+	Volume.cpp
+;
+
+LinkSharedOSLibs obfs : /boot/develop/lib/x86/_KERNEL_ ;