std::vector -> std::array for constant

[Dushistov]

std::vector is not very well suited for static, constant arrays.
Since creating it from a std::initializer_list requires memory allocation,
modern C++ compilers miss out on many optimizations.
In particular, compilers are forced to insert a call to a global
atomic variable and a bunch of code for initialization of std::vector.
Plus access to heap memory cause cache misses.
For example for this function:

bool f(const int *arr, int x)
{
    static std::vector<Foo> const values = {A, B, C};
    for (auto v : values) {
        if (arr[static_cast<size_t>(v)] == x)
            return true;
    }
    return false;
}

compiler generates ~60 instructions (gcc 10.2 -O3 -march=native),
if replace std::vector with std::array the result code contains only 9 instructions.