The Makefile stanzas for building the gnat tools cross is somehow confused and mixing use of the newly built cross compiler and the native compiler. The gnat tools should be built to execute on the host. I posted a message about this to the gcc mailing list (http://gcc.gnu.org/ml/gcc/2005-01/msg00904.html). I will attach a section from a log.
-- Summary: gnat tools not buildable cross Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: ada AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: joel at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org,laurent at guerby dot net GCC build triplet: i686-pc-linux-gnu GCC host triplet: i686-pc-linux-gnu GCC target triplet: *-rtems* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19489