This bug is solved in the C front-end (bug 4076).
The original patch also addressed the C++ front-end
http://gcc.gnu.org/ml/gcc-patches/2007-03/msg00171.html
However, some issues were raised about functions in anonymous namespaces:
http://gcc.gnu.org/ml/gcc-patches/2007-03/msg01103.html
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Summary: -Wunused doesn't warn about static function only called
by itself.
Product: gcc
Version: unknown
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: manu at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32562