[Bug d/109108] New: d: Undefined reference to lambda in private enum

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109108

            Bug ID: 109108
           Summary: d: Undefined reference to lambda in private enum
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: d
          Assignee: ibuclaw at gdcproject dot org
          Reporter: ibuclaw at gcc dot gnu.org
  Target Milestone: ---

Similar to pr108055.  Lambdas should be emitted in every module they are
referenced from.

```
import other;
void main()
{
    auto a = callFun(1);
}
```

```
private enum int function(ref int)[] funs =
[
    0: (ref idx) => 0,
    1: (ref idx) => 1,
];

int callFun(I)(I idx)
{
    return funs[idx](idx);
}
```

Only compiling the "main" module results in linker errors.
---
$ gdc test.d -Wl,--demangle=dlang
/usr/x86_64-pc-linux-gnu/bin/ld: /tmp/ccDW8iNw.o: in function
`other.callFun!(int).callFun(int)':
test.d:(.text+0x4b): undefined reference to
`other.__lambda4!(int).__lambda4(ref int)'
test.d:(.text+0x56): undefined reference to
`other.__lambda5!(int).__lambda5(ref int)'
collect2: error: ld returned 1 exit status