The fedora guidelines state that when a package provides static libraries, you can put then in a -devel subpackage. When doing this you also have to have a virtual Provide for the static package. As you package provides /usr/lib/libfl.a and /usr/lib/libl.a it would be nice to have a flex-static to link with
The intent of this particular guideline is that preferably only dynamic libraries should be distributed/installed, and static ones only on request when necessary, for special purposes. Flex only distributes static library. This library contains only two symbols, both of them functions so simple and stable, that normal arguments for DSO don't really apply here. Dividing package to two makes no sense here. If you need -lfl, you almost always need also flex itself (headers & code generator). If you need flex itself, you very often need -lfl.