Expected constexpr on detail::EnableBitmask<Enum> operator...(Enum X, Enum Y)

[phprus]

Describe the bug
C++11 17.5.2.1.3 Bitmask types:
constexpr bitmask operator&(bitmask X, bitmask Y)
constexpr bitmask operator|(bitmask X, bitmask Y)
constexpr bitmask operator^(bitmask X, bitmask Y)
constexpr bitmask operator~(bitmask X)

To Reproduce
Using the perm_options operator... in a constexpr function results in a compilation error.

Expected behavior
Compiling without error.

[gulrak]

Seems I missed that, thanks for reporting, will look into it. Just a few minutes too late for v1.3.8.

[gulrak]

This is now part of release v1.3.10