Fix error: old-style function definition

https://rubyci.s3.amazonaws.com/debian-riscv64/ruby-master/log/20220122T050018Z.log.html.gz#miniruby
```
compiling vm_trace.c
vm_trace.c: In function 'rb_vm_memsize_postponed_job_buffer':
vm_trace.c:1599:1: error: old-style function definition [-Werror=old-style-definition]
 1599 | rb_vm_memsize_postponed_job_buffer()
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

1 files changed, 1 insertions, 1 deletions

diff --git a/vm_trace.c b/vm_trace.c
index 7f6a60b0cb..5fa9acd487 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -1596,7 +1596,7 @@ rb_vm_memsize_workqueue(struct list_head *workqueue)
 // Used for VM memsize reporting. Returns the total size of the postponed job
 // buffer that was allocated at initialization.
 size_t
-rb_vm_memsize_postponed_job_buffer()
+rb_vm_memsize_postponed_job_buffer(void)
 {
     return sizeof(rb_postponed_job_t) * MAX_POSTPONED_JOB;
 }