Incorporate MSVC's __declspec(noalias)

[OfekShilon]

Microsoft's __declspec(noalias) is documented as:

noalias means that a function call doesn't modify or reference visible global state and only modifies the memory pointed to directly by pointer parameters (first-level indirections).

So it is analogous to gcc/clang __attribute__((const)). Currently HEDLEY_CONST does not generate it.

[apache-hb]

According to the gcc docs.
const functions should never take pointer or, in C++, reference arguments.

This seems to conflict with msdn noalias docs
noalias means that a function call doesn't modify or reference visible global state and only modifies the memory pointed to directly by pointer parameters (first-level indirections).

These appear to be incompatible, im not sure HEDLEY_CONST would be a correct place for __declspec(noalias)