This port needs C++11-compatible compiler. Add USES=compiler:c++11-lang
to fix build on GCC-based architectures:

/usr/local/include/sigc++-2.0/sigc++/visit_each.h:22:23: error: type_traits: No such file or directory

While here, pet portlint.

PR: 236986
Submitted by: Piotr Kubaj
Approved by: maintainer