disallow empty struct-declaration-list

[WalterBright]

@thewilsonator got this right. I misread the C11 spec, conflating struct-declarator-list with struct-declaration-list

[dlang-bot]

Thanks for your pull request, @WalterBright!

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[thewilsonator]

this really ought to have a fail compilation test.

[WalterBright]

It's best to defer fail_compilation tests for now. As the implementation is in flux, these tend to be big maintenance problems, enough to provide an incentive not to do the right thing in the code. Much better when the disruptive changes settle down.

On the other hand, we know what must compile successfully, and that isn't going to change, so writing those tests is appropriate now.

[ibuclaw]

It is accepted as a GNU/Clang extension though (we have support code in D to handle empty C++ structs), but I guess we'll wait and see if it shows up in the wild.