tools lib traceevent: Use global 'O' processing code

Using global 'O' processing code because it's already setup due to the
scripts/Makefile.include include.

Using global variable OUTPUT instead of the local BUILD_OUTPUT.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1387460527-15030-10-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/Makefile

@@ -83,18 +83,13 @@ ifeq ("$(origin O)", "command line")
 endif
 
 ifeq ($(BUILD_SRC),)
-ifneq ($(BUILD_OUTPUT),)
+ifneq ($(OUTPUT),)
 
 define build_output
-	$(if $(VERBOSE:1=),@)+$(MAKE) -C $(BUILD_OUTPUT) 	\
-	BUILD_SRC=$(CURDIR) -f $(CURDIR)/Makefile $1
+	$(if $(VERBOSE:1=),@)+$(MAKE) -C $(OUTPUT) \
+	BUILD_SRC=$(CURDIR)/ -f $(CURDIR)/Makefile $1
 endef
 
-saved-output := $(BUILD_OUTPUT)
-BUILD_OUTPUT := $(shell cd $(BUILD_OUTPUT) && /bin/pwd)
-$(if $(BUILD_OUTPUT),, \
-     $(error output directory "$(saved-output)" does not exist))
-
 all: sub-make
 
 $(MAKECMDGOALS): sub-make
@@ -106,7 +101,7 @@ sub-make: force
 # Leave processing to above invocation of make
 skip-makefile := 1
 
-endif # BUILD_OUTPUT
+endif # OUTPUT
 endif # BUILD_SRC
 
 # We process the rest of the Makefile if this is the final invocation of make