[Bug c++/50785] [C++0x][constexpr] static constexpr double undefined reference

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50785

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-10-19 
08:34:45 UTC ---
The definition is required, see [class.static.data] p3

"A static data member of literal type can be declared in the class definition
with the constexpr specifier; [...] The member shall still be defined in a
namespace scope if it is odr-used (3.2) in the program and the namespace scope
definition shall not contain an initializer."