[Bug c++/84843] New: [8 Regression] C++ ICE on builtin redefinition since r258391

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84843

            Bug ID: 84843
           Summary: [8 Regression] C++ ICE on builtin redefinition since
                    r258391
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

extern "C" int __atomic_compare_exchange (int x, int y) { return x + y; }
ICEs starting with the above revision in:
0x8fc5c2 start_preparsed_function(tree_node*, tree_node*, int)
        ../../gcc/cp/decl.c:15060
0x8fe24c start_function(cp_decl_specifier_seq*, cp_declarator const*,
tree_node*)
        ../../gcc/cp/decl.c:15287
0x9e01b3 cp_parser_function_definition_from_specifiers_and_declarator
        ../../gcc/cp/parser.c:26700
0x9d1e88 cp_parser_init_declarator
        ../../gcc/cp/parser.c:19502
0x9c5be7 cp_parser_simple_declaration
        ../../gcc/cp/parser.c:13057
0x9c5750 cp_parser_block_declaration
        ../../gcc/cp/parser.c:12882
0x9c54d2 cp_parser_declaration
        ../../gcc/cp/parser.c:12780