[Dlang-internal] Detect CTFE in AssignExp:semantic

[Martin Nowak via Dlang-internal]

On Wednesday, 11 January 2017 at 17:10:15 UTC, Andrei 
Alexandrescu wrote:
>> Calls for the old dmd<->C-API are very different from template 
>> functions
>> calls, e.g. take a look at how _xOpEquals is called.
>> https://github.com/dlang/dmd/blob/538a895157acdbbfc5869791f9504f7e86b4fdd0/src/clone.d#L496
>

Sorry, it's not the best example, b/c that also generates a 
function.
Added inline comments on 
https://github.com/somzzz/dmd/commit/8bccc49ba661567c523545650aad30c01fd25090 which isn't far off.

> Or perhaps that's why the error with reading the variable 
> during compilation?

Not sure where that comes from, there are unrelated changes as 
well.