Log Message:
Update to libtool-2.2.6b. This switches libtool to the new main branch.
Changes are many, important for pkgsrc:
- much higher speed (up to 30% faster for the overall build of libX11)
- less magic for detection of the tag

The pkgsrc integration of f2c has been changed to be more sane.
libtool itself now depends on the f2c frontend to use proper
auto-configuration and only fakes up the library. This part is
encapsulated in mk/compiler/f2c.mk.