Add compiler:c++17-lang to USES to fix build on GCC-based systems:
cc1plus: error: unrecognized command line option "-Wno-class-memaccess" cc1plus: error: unrecognized command line option "-std=c++17" cc1plus: error: unrecognized command line option "-std=gnu++1z"
Approved by: portmgr (tier-2 blanket)