https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78349
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- I think this is a known issue and intentionally not fixed on the GCC 5 branch (but it is fixed for GCC 6). N.B. GNU nm has a -C option to demangle so you don't need c++filt.
