Found the following significant warnings:
  ./curl-common.h:61:22: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  ./curl-common.h:65:18: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  handle.c:36:18: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  handle.c:107:43: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  handle.c:213:18: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  handle.c:450:19: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  handle.c:488:21: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  ieproxy.c:165:18: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  ieproxy.c:173:21: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:14:27: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:16:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:30:24: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:34:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:36:25: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:39:28: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:40:28: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:41:28: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  init.c:82:32: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  interrupt.c:13:22: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  multi.c:234:17: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  reflist.c:3:18: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  ssl.c:11:32: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  version.c:6:20: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  winidn.c:69:41: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  writer.c:41:21: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
See '/home/hornik/tmp/R.check/r-devel-clang/Work/PKGS/curl.Rcheck/00install.out' for details.