Found the following significant warnings:
  2k.c:25:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  2k.c:27:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  2k.c:169:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  2k.c:230:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  2k.c:299:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  2k.c:314:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:341:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:343:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:345:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:385:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:387:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:408:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gcontrol_c.c:410:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:39:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:40:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:41:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:47:3: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:111:9: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:137:10: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:163:18: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:187:10: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:249:9: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gif_c.c:279:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  hap_c.c:1348:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  gdef.h:31:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:161:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:175:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:187:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:217:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:250:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:330:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:407:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:436:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:520:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:600:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:640:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:672:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:852:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:971:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:998:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1038:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1076:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1220:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1289:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1424:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1539:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1560:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1584:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1626:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  makeped_c.c:1649:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
See ‘/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/gap.Rcheck/00install.out’ for details.