Found the following significant warnings:
  ../inst/include/CImg.h:193:5: warning: 'long long' is a C++11 extension [-Wc++11-long-long]
  ../inst/include/CImg.h:13559:29: warning: multiple unsequenced modifications to 'ptrs' [-Wunsequenced]
  ../inst/include/CImg.h:13738:19: warning: multiple unsequenced modifications to 'ptrs' [-Wunsequenced]
  ../inst/include/CImg.h:22316:23: warning: unsequenced modification and access to 'right' [-Wunsequenced]
  ../inst/include/CImg.h:29395:35: warning: unsequenced modification and access to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29395:35: warning: multiple unsequenced modifications to '_n3x' [-Wunsequenced]
  ../inst/include/CImg.h:29395:35: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:29415:40: warning: unsequenced modification and access to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29415:40: warning: multiple unsequenced modifications to '_n3x' [-Wunsequenced]
  ../inst/include/CImg.h:29415:40: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:29435:35: warning: multiple unsequenced modifications to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29435:35: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:29449:40: warning: multiple unsequenced modifications to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29449:40: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:29467:35: warning: multiple unsequenced modifications to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29467:35: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:29478:40: warning: multiple unsequenced modifications to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:29478:40: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:30531:19: warning: unsequenced modification and access to 'right' [-Wunsequenced]
  ../inst/include/CImg.h:31964:17: warning: multiple unsequenced modifications to '_n2x' [-Wunsequenced]
  ../inst/include/CImg.h:31964:17: warning: unsequenced modification and access to '_n1x' [-Wunsequenced]
  ../inst/include/CImg.h:44923:18: warning: unsequenced modification and access to 'err' [-Wunsequenced]
  ../inst/include/CImg.h:44931:18: warning: unsequenced modification and access to 'err' [-Wunsequenced]
  ../inst/include/CImg.h:44941:22: warning: unsequenced modification and access to 'err' [-Wunsequenced]
  ../inst/include/CImg.h:45125:18: warning: unsequenced modification and access to 'err' [-Wunsequenced]
  ../inst/include/CImg.h:45133:18: warning: unsequenced modification and access to 'err' [-Wunsequenced]
  ../inst/include/CImg.h:45142:20: warning: unsequenced modification and access to 'err' [-Wunsequenced]
See ‘/Users/ripley/R/packages/tests-devel/imager.Rcheck/00install.out’ for details.