ipc3: check alignment of ext data

[cujomalainey]

Sizes are not currently checked for alignment, this can generated unaligned pointers for aligned types which is undefined behaviour.

[marc-hb]

I was really wondering how the GCC aligned attribute and extension could result in "undefined behavior" since it is not part of the standard and no undefined behavior is mentioned in the documentation:
https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html

I think the answer is: this is now part of the standard! But under a different name:
https://en.cppreference.com/w/c/language/_Alignas

So the GCC extension has likely been "retrofitted" to behave like the standard alignas - undefined behaviors included?

[lgirdwood]

This will fix for v2.11, I think we made a mistake using bytes for size in IPC3 when we always use words for size/alignment. Oh well.

[cujomalainey]

Whoops, there is an IS_ALIGNED macro, I must have pushed the wrong branch. I'll send a fix today.

[marc-hb]

Whoops, there is an IS_ALIGNED macro, I must have pushed the wrong branch. I'll send a fix today.

Maybe an opportunity to add some "TODOs: switch to the new standard" next to these macro definitions?