Share ruby_sighandler_t definition

error.c

@@ -599,7 +599,7 @@ rb_bug(const char *fmt, ...)
 }
 
 void
-rb_bug_for_fatal_signal(RETSIGTYPE (*default_sighandler)(int), int sig, const void *ctx, const char *fmt, ...)
+rb_bug_for_fatal_signal(ruby_sighandler_t default_sighandler, int sig, const void *ctx, const char *fmt, ...)
 {
     const char *file = NULL;
     int line = 0;

signal.c

@@ -507,13 +507,8 @@ static struct {
 volatile unsigned int ruby_nocldwait;
 #endif
 
-#ifdef __dietlibc__
-#define sighandler_t sh_t
-#else
 #define sighandler_t ruby_sighandler_t
-#endif
 
-typedef RETSIGTYPE (*sighandler_t)(int);
 #ifdef USE_SIGALTSTACK
 typedef void ruby_sigaction_t(int, siginfo_t*, void*);
 #define SIGINFO_ARG , siginfo_t *info, void *ctx

vm_core.h

@@ -1624,7 +1624,8 @@ extern void rb_vmdebug_debug_print_post(const rb_execution_context_t *ec, const
 #define SDR() rb_vmdebug_stack_dump_raw(GET_EC(), GET_EC()->cfp)
 #define SDR2(cfp) rb_vmdebug_stack_dump_raw(GET_EC(), (cfp))
 void rb_vm_bugreport(const void *);
-NORETURN(void rb_bug_for_fatal_signal(RETSIGTYPE (*default_sighandler)(int), int sig, const void *, const char *fmt, ...));
+typedef RETSIGTYPE (*ruby_sighandler_t)(int);
+NORETURN(void rb_bug_for_fatal_signal(ruby_sighandler_t default_sighandler, int sig, const void *, const char *fmt, ...));
 
 /* functions about thread/vm execution */
 RUBY_SYMBOL_EXPORT_BEGIN