Update test to conditionally disable constexpr evaluation
Add workaround for vardiac expansion on gcc 4.6
Add workaround for incomplete decltype on gcc 4.6
Add some more workarounds for gcc
Add mangle type casting to returns macro to workaround no mangling overload in gcc 4.6
Update the delegate constructor for gcc 4.6 to workaround no argument pack expansion in templates
Use workarounds for mangling overloads
Fix mangling overloads for placeholders