editors/wxhexeditor: fix build with GCC-based architectures

Add USES=compiler:c++11-lang to fix:
/usr/local/include/wx-3.0/wx/strvararg.h:350: error: ISO C++ forbids declaration of 'is_enum' with no typeIn file included from /usr/local/include/wx-3.0/wx/string.h:46,

Approved by: mentors (implicit approval)