[Bug c++/105418] debug_tree does not support well for std::construct_at

["guojiufu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105418

--- Comment #5 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
0x1089f887 dump_substitution
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/error.cc:1654
0x108a1c2f dump_function_decl
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/error.cc:1817
0x1089e187 dump_decl
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/error.cc:1385
0x108aa8df decl_as_string(tree_node*, int)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/error.cc:3146
0x1094d6ef trees_out::insert(tree_node*, walk_kind)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:4801
0x1096300f trees_out::decl_node(tree_node*, walk_kind)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:8582
0x10965da3 trees_out::tree_node(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:9104
0x109542c7 trees_out::core_vals(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:5924
0x10959d4f trees_out::tree_node_vals(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:7074
0x10964dab trees_out::tree_value(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:8911
0x10965ddf trees_out::tree_node(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:9109
0x109542c7 trees_out::core_vals(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:5924
0x10959d4f trees_out::tree_node_vals(tree_node*)
        /home/guojiufu/gcc/gcc-mainline-base/gcc/cp/module.cc:7074
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Hi Andrew and Richard,

Thanks a lot! 
This issue happens when calling debug_tree/decl_as_string manually inside FE. 
At where overloaded functions (::new) are not resolved yet, and then cause
'tsubst' to be called. 
I see, it is not a good place to use debug_tree.