perf tools: Honor parallel jobs

We need to hand down parallel build options like the internal make
--jobserver-fds one so that parallel builds can also happen when
building perf from the toplevel directory.

Make it so #1!

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1361374353-30385-3-git-send-email-bp@alien8.de
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/scripts/Makefile.include

@@ -70,7 +70,7 @@ ifndef V
 	QUIET_BISON    = @echo '   ' BISON $@;
 
 	descend = \
-		@echo '   ' DESCEND $(1); \
+		+@echo '   ' DESCEND $(1); \
 		mkdir -p $(OUTPUT)$(1) && \
 		$(MAKE) $(COMMAND_O) subdir=$(if $(subdir),$(subdir)/$(1),$(1)) $(PRINT_DIR) -C $(1) $(2)
 endif