Include qemu/main-loop.h less

In my "build everything" tree, changing qemu/main-loop.h triggers a
recompile of some 5600 out of 6600 objects (not counting tests and
objects that don't depend on qemu/osdep.h).  It includes block/aio.h,
which in turn includes qemu/event_notifier.h, qemu/notify.h,
qemu/processor.h, qemu/qsp.h, qemu/queue.h, qemu/thread-posix.h,
qemu/thread.h, qemu/timer.h, and a few more.

Include qemu/main-loop.h only where it's needed.  Touching it now
recompiles only some 1700 objects.  For block/aio.h and
qemu/event_notifier.h, these numbers drop from 5600 to 2800.  For the
others, they shrink only slightly.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190812052359.30071-21-armbru@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
diff --git a/block.c b/block.c
index cbd8da5..1b67b49 100644
--- a/block.c
+++ b/block.c
@@ -30,6 +30,7 @@
 #include "block/qdict.h"
 #include "qemu/error-report.h"
 #include "module_block.h"
+#include "qemu/main-loop.h"
 #include "qemu/module.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"