audio/alure: fix build on GCC architectures

C++11 compiler is necessary:
/usr/local/lib/libopenal.so: undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_mutate(unsigned long, unsigned long, char const*, unsigned long)@GLIBCXX_3.4.21'

Approved by: mentors (implicit approval)