Found the following significant warnings:
  ./rlang/cnd.h:9:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ./rlang/cnd.h:27:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ./rlang/session.h:6:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ./rlang/stack.h:7:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  ./rlang/stack.h:13:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  utils.h:384:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  order-groups.h:108:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  subscript.h:32:23: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  subscript-loc.h:37:22: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  fill.c:205:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  fill.c:241:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:99:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:107:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  names.c:206:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  names.c:415:13: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  names.c:853:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  order-groups.c:18:20: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:8:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:15:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:216:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:217:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:232:20: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:236:20: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:292:20: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rep.c:301:20: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/arg.c:5:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/call.c:65:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/cnd.c:106:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/cnd.c:147:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/dyn-array.c:122:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/env.c:275:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/env.c:281:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/fn.c:28:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/globals.c:58:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/obj.c:72:16: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/quo.c:8:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/session.c:19:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/session.c:28:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/stack.c:19:8: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/stack.c:77:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/sym.c:56:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rlang/vendor.c:5:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  utils.c:242:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  utils.c:1616:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  version.c:25:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
See ‘/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/vctrs.Rcheck/00install.out’ for details.