openrc, openrc-run: Fix -Wstrict-prototypes

These become fine with C23 because () starts to mean (void) then, but for
previous language versions, it's deprecated, and it causes an annoying
warning when building with Clang by default.

Plus, GCC lacks specific flags to trigger what C23 *does* ban, so a lot
of people are going around building with -Wstrict-prototypes, so let's
just fix this to be consistent with the rest of the codebase anyway
to fend off false positive reports.

src/openrc-run/openrc-run.c

@@ -161,7 +161,7 @@ handle_signal(int sig)
 }
 
 static void
-unhotplug()
+unhotplug(void)
 {
 	char *file = NULL;
 
@@ -788,7 +788,7 @@ svc_start_deps(void)
 	services = NULL;
 }
 
-static void svc_start_real()
+static void svc_start_real(void)
 {
 	bool started;
 	RC_STRING *svc, *svc2;

src/openrc/rc.c

@@ -452,7 +452,7 @@ handle_signal(int sig)
 }
 
 static void
-do_sysinit()
+do_sysinit(void)
 {
 	struct utsname uts;
 	const char *sys;