PR c++/27329
        PR c++/26938
        * cp-tree.h (redeclare_class_template): Adjust declaration
        to return bool instead of void.
        * pt.c (redeclare_class_template): Update definition. Return
        false on error.
        * decl.c (xref_tag): Return error_mark_node if redeclare_class_template
        returned false.

        * g++.dg/template/crash58.C: New test.
        * g++.dg/template/crash59.C: New test.
        * g++.dg/parse/crash28.C: Adjust error markers.
        * g++.dg/template/crash34.C: Likewise.
        * g++.dg/template/friend31.C: Likewise.
        * g++.dg/template/crash32.C: Likewise.

From-SVN: r117205