core.memory.GC allocation functions are not marked as @safe

[Eduard Staniloiu]

Hello, everybody.

While working at [this 
PR](https://github.com/dlang/phobos/pull/6811/files), reviews are 
welcome :D, I noticed that none of the `core.memory.GC` 
allocation functions are marked as `@safe`.

I believe that `GC.malloc`, `GC.calloc`, `GC.qalloc` and 
`GC.expand` should all be `@safe`, as they either give you the 
**fresh** memory that you requested, or they fail.

What are your thoughts on this?

Cheers,
Edi