Library does not compile with G++ under OS X

[nicola-gigante]

With G++ version 4.8 or 4.9 on OS X, installed from Homebrew, the library does not compiler:

optional.hpp: In function 'void std::experimental::fail(const char*, const char*, unsigned int)':
optional.hpp:211:29: error: '_assert' was not declared in this scope
     _assert(expr, file, line);

If I add an underscore to call __assert instead of _assert everything works. It seems that it fails to recognize that it is using the GNU library

[akrzemi1]

Does it work now?