Feature Request: Better Warning for Invalid `alignas(...)`

[Ian_Mallett1]

If you do something like `alignas(sizeof(NonPoTStruct))`, you get:
error : invalid alignment value specified by attribute

This says what is wrong, but isn't very useful. As a hopefully minor tweak, how about something like:
error : invalid alignment value (12) specified by attribute (not a power-of-two)

Would have saved me a bit of time.

[KitturGanesh]

Thanks Ian, yes makes sense. I'll file the feature request with the developers accordingly, appreciate much.

Kittur