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 <[e-mail]>
Signed-off-by: Adrian Hunter <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Makefile.perf

···
 	$(Q)$(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 $@ $<