stubs: Move qemu_timer_notify_cb() and remove qemu_notify_event() stub

When cross-compiling with MinGW, there are sometimes some weird linker
errors like:

ibqemuutil.a(util_main-loop.c.obj): In function `qemu_notify_event':
/builds/huth/qemu/build/../util/main-loop.c:139: multiple definition of
 `qemu_notify_event'
libqemuutil.a(stubs_notify-event.c.obj):/builds/huth/qemu/stubs/notify-event.c:5:
 first defined here
collect2: error: ld returned 1 exit status
/builds/huth/qemu/rules.mak:88: recipe for target 'tests/test-timed-average.exe'
 failed

It seems like it works better when the qemu_timer_notify_cb() stub (which
calls qemu_notify_event()) is in a separate file - then we can also even
remove the qemu_notify_event() stub now.

This patch is based on ideas from the patch "stubs: Remove qemu_notify_event()"
by Philippe Mathieu-Daudé and the patch "cpu-timers, icount: new modules" from
Claudio Fontana.

Message-Id: <20200902102433.304737-1-thuth@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

stubs/cpu-get-icount.c

@@ -14,8 +14,3 @@ int64_t cpu_get_icount_raw(void)
 {
     abort();
 }
-
-void qemu_timer_notify_cb(void *opaque, QEMUClockType type)
-{
-    qemu_notify_event();
-}

stubs/meson.build

@@ -24,9 +24,9 @@ stub_ss.add(files('machine-init-done.c'))
 stub_ss.add(files('migr-blocker.c'))
 stub_ss.add(files('monitor.c'))
 stub_ss.add(files('monitor-core.c'))
-stub_ss.add(files('notify-event.c'))
 stub_ss.add(files('pci-bus.c'))
 stub_ss.add(files('pci-host-piix.c'))
+stub_ss.add(files('qemu-timer-notify-cb.c'))
 stub_ss.add(files('qmp_memory_device.c'))
 stub_ss.add(files('qtest.c'))
 stub_ss.add(files('ram-block.c'))

stubs/notify-event.c

@@ -1,6 +0,0 @@
-#include "qemu/osdep.h"
-#include "qemu/main-loop.h"
-
-void qemu_notify_event(void)
-{
-}

stubs/qemu-timer-notify-cb.c

@@ -0,0 +1,8 @@
+#include "qemu/osdep.h"
+#include "sysemu/cpus.h"
+#include "qemu/main-loop.h"
+
+void qemu_timer_notify_cb(void *opaque, QEMUClockType type)
+{
+    qemu_notify_event();
+}