perf build: Suppress 'rm dlfilter' build message

The following build message:

	rm dlfilters/dlfilter-test-api-v0.o

is unwanted.

The object file is being treated as an intermediate file and being
automatically removed. Mark the object file as .SECONDARY to prevent
removal and hence the message.

Requested-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lore.kernel.org/lkml/20210930062849.110416-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -789,6 +789,8 @@ $(OUTPUT)dlfilters/%.o: dlfilters/%.c include/perf/perf_dlfilter.h
 	$(Q)$(MKDIR) -p $(OUTPUT)dlfilters
 	$(QUIET_CC)$(CC) -c -Iinclude $(EXTRA_CFLAGS) -o $@ -fpic $<
 
+.SECONDARY: $(DLFILTERS:.so=.o)
+
 $(OUTPUT)dlfilters/%.so: $(OUTPUT)dlfilters/%.o
 	$(QUIET_LINK)$(CC) $(EXTRA_CFLAGS) -shared -o $@ $<