Fix FTBFS when using -pedantic compiler flag.

I am attaching an incremental git-am ready patch to go on top your Git HEAD,
to fix all sorts of issues and make this conforming C99 with default
options set,
and fix another load of warnings you receive when setting the compiler
to pick the nits,
-pedantic-errors -std=c99 (or c11, c18, c2x).
It changes many void * to uint8_t * to make the "increment by bytes"
explicit.
You can't do:

void *foo;
// ...
foo += 2.

src/loop.c

@@ -19,7 +19,7 @@
 #ifdef HAVE_LOOP
 static ssize_t loop_make_probe(u32 uid);
 
-void loop_send_probes()
+void loop_send_probes(void)
 {
    struct server *serv;
    struct randfd_list *rfds = NULL;