Compile-time variadic equality

[Nordlöw]

I'm looking for a function (that probably should be placed in 
std.meta) named something like `areEqual` that checks whether all 
it's arguments are equal or not.

Is there such as function already in Phobos?

My usage is

static if (allEqual!(staticMap!(ElementEncodingType, Rs)))
{
     // compare Rs byCodeUnit
}