I noticed this when changing libgfortran/io/io.h didn't cause a rebuild. This patch <http://gcc.gnu.org/ml/gcc-patches/2004-05/msg02026.html> by Andreas Jäger turned of automatic dependency tracking for libgfortran.
Since I don't have access to a multilibbed target, I can't verify that turning on automatic dependecy generation doesn't break them. -- Summary: Mo automatic dependencies in libgfortran Product: gcc Version: 4.0.0 Status: UNCONFIRMED Keywords: build Severity: normal Priority: P2 Component: bootstrap AssignedTo: pbrook at gcc dot gnu dot org ReportedBy: tobi at gcc dot gnu dot org CC: aj at suse dot de,gcc-bugs at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19273