Found the following significant warnings:
  clipper.cpp:4388:22: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4388:25: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4388:32: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4388:35: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:7: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:12: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:20: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:25: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:33: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:38: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:41: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:47: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:52: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4389:55: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:11: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:16: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:26: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:31: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:41: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:46: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:49: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:55: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:60: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4390:63: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:39: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:42: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:50: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:56: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:69: warning: invalid UTF-8 in comment [-Winvalid-utf8]
  clipper.cpp:4391:74: warning: invalid UTF-8 in comment [-Winvalid-utf8]
See '/home/hornik/tmp/R.check/r-devel-clang/Work/PKGS/polyclip.Rcheck/00install.out' for details.