[Bug c++/126835] New: ICE on templated #pragma omp declare mapper with -fopenmp-simd

[s.kimura.h41104 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126835

            Bug ID: 126835
           Summary: ICE on templated #pragma omp declare mapper with
                    -fopenmp-simd
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: s.kimura.h41104 at gmail dot com
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/5Wz7b3xqb

Reproducer:
```
struct S {};

template <typename T> void foo() {
  int y;
#pragma omp declare mapper(T var) map(always, to : var, y)
}

void bar() { foo<S>(); }
```

Backtrace:
<source>: In instantiation of 'void foo() [with T = S]':
<source>:8:20:   required from here
    8 | void bar() { foo<S>(); }
      |              ~~~~~~^~
<source>:5:30: internal compiler error: in copy_linkage, at cp/decl2.cc:4078
    5 | #pragma omp declare mapper(T var) map(always, to : var, y)
      |                              ^~~
0x2bae358 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x2ba2f9b internal_error(char const*, ...)
        ???:0
0xb427ee fancy_abort(char const*, int, char const*)
        ???:0
0xc61b8c get_guard(tree_node*)
        ???:0
0xc5444f cp_finish_decl(tree_node*, tree_node*, bool, tree_node*, int,
cp_decomp*)
        ???:0
0xdfd61d instantiate_decl(tree_node*, bool, bool)
        ???:0
0xe0750a instantiate_pending_templates(int)
        ???:0
0xc68fd8 c_parse_final_cleanups()
        ???:0
0xf2b998 c_common_parse_file()
        ???:0


This ICE goes back to gcc-16:
https://godbolt.org/z/djWK8s7aT