Status status = __traits(compilesReportError, {string b=10;}) => status.msg=Error: cannot....

[Timothee Cour]

is there any way to get error from speculative execution (`__traits(
compiles, ...)`)? would be useful in tests; If not currently how hard
would that be to implement? eg:

```

struct Status{bool ok; string msg;}

Status status = __traits(compilesReportError, {string b=10;})
assert(!status.ok);
assert(status.msg==`main.d(15) Error: cannot implicitly convert
expression 10 of type int to string`);
```