Found the following significant warnings:
  rJava.h:123:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rJava.h:167:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rglue.c:39:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rglue.c:1214:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rglue.c:1225:10: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:713:16: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 2 has type ‘uintptr_t’ {aka ‘long unsigned int’} [-Wformat=]
  init.c:751:10: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  init.c:762:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  loader.c:34:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  otables.c:11:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rJava.c:14:13: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rJava.c:142:14: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  registration.c:6:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  tools.c:109:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  tools.c:131:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  tools.c:141:11: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.h:13:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.h:14:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.h:17:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.h:25:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.h:26:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.h:27:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rinit.h:5:1: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.c:39:9: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.c:144:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.c:149:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rcallbacks.c:166:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  Rinit.c:88:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.c:16:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.c:27:5: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
  rjava.c:47:6: warning: function declaration isn’t a prototype [-Wstrict-prototypes]
See ‘/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/rJava.Rcheck/00install.out’ for details.
* used C compiler: ‘gcc-13 (Debian 13.2.0-5) 13.2.0’