Makefile: Keep trace-events-subdirs ordered

Adding the same directory multiple times to trace-events-subdirs
might trigger build failures, in particular when using the LTTng
Userspace Tracer library as backend.

For example when using two times the hw/core/ directory:

    $ ./configure --enable-trace-backends=ust && make
   [...]
     CC      trace-ust-all.o
   In file included from trace-ust-all.h:13,
                    from trace-ust-all.c:13:
   trace-ust-all.h:35151:1: error: redefinition of ‘__tracepoint_cb_qemu___loader_write_rom’
   35151 | TRACEPOINT_EVENT(
         | ^~~~~~~~~~~~~~~~
   trace-ust-all.h:31791:1: note: previous definition of ‘__tracepoint_cb_qemu___loader_write_rom’ was here
   31791 | TRACEPOINT_EVENT(
         | ^~~~~~~~~~~~~~~~

To ease review and reduce likelihood of merge failures (see [*]),
keep trace-events-subdirs ordered when possible, following eb7ccb3c.

[*] https://www.mail-archive.com/qemu-devel@nongnu.org/msg671007.html
    Duplicate trace-events-subdirs entries generates duplicated
    symbols when using the LTTng Userspace Tracer library.
Reviewed-by: NDamien Hedde <damien.hedde@greensocs.com>
Signed-off-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200116114339.30670-1-philmd@redhat.com
Message-Id: <20200116114339.30670-1-philmd@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

Makefile.objs

@@ -132,8 +132,8 @@ trace-events-subdirs += nbd
 trace-events-subdirs += scsi
 endif
 ifeq ($(CONFIG_SOFTMMU),y)
-trace-events-subdirs += chardev
 trace-events-subdirs += audio
+trace-events-subdirs += chardev
 trace-events-subdirs += hw/9pfs
 trace-events-subdirs += hw/acpi
 trace-events-subdirs += hw/alpha
@@ -181,6 +181,7 @@ trace-events-subdirs += migration
 trace-events-subdirs += net
 trace-events-subdirs += ui
 endif
+trace-events-subdirs += hw/core
 trace-events-subdirs += hw/display
 trace-events-subdirs += qapi
 trace-events-subdirs += qom
@@ -193,7 +194,6 @@ trace-events-subdirs += target/riscv
 trace-events-subdirs += target/s390x
 trace-events-subdirs += target/sparc
 trace-events-subdirs += util
-trace-events-subdirs += hw/core
 
 trace-events-files = $(SRC_PATH)/trace-events $(trace-events-subdirs:%=$(SRC_PATH)/%/trace-events)