Found the following significant warnings:
  curl-common.h:61:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  curl-common.h:65:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  handle.c:36:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  handle.c:107:28: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  handle.c:213:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  handle.c:450:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  handle.c:488:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ieproxy.c:165:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ieproxy.c:173:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:14:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:16:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:30:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:34:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:36:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:39:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:40:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:41:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:82:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  interrupt.c:13:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  multi.c:234:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  reflist.c:3:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ssl.c:11:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  version.c:6:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  winidn.c:69:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  writer.c:41:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
See ‘/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/curl.Rcheck/00install.out’ for details.