Take:
```
void f(int a)
{
  [& const a](){};
}
```
The current error message is:
```
<source>: In function 'void f(int)':
<source>:3:5: error: expected ',' before 'const'
    3 |   [& const a](){};
      |     ^~~~~~
      |     ,
<source>:3:6: error: expected identifier before 'const'
    3 |   [& const a](){};
      |      ^~~~~
```
clang gives:
```
<source>:3:6: error: expected variable name or 'this' in lambda capture list
  [& const a](){};
     ^
```
Which is slightly better.
but I think we could do better and say qualifers should not be in the capture list.