only use `-nostdinc++` on c++ files

This is a follow-up to d27ef1aaef8ac12801ba4e6c2ed748c7151096a7
and avoids compiler warnings:

    warning: argument unused during compilation: '-nostdinc++'
20b2457388Michael Dusan committed on 4/12/2020, 5:03:27 AMparentd27ef1a
1 file changedLine totals unavailable