perf tools: Correct Makefile.include

It looks at O= and adjusts the $(OUTPUT) variable based on what the
output directory will be. However, when O is defined but empty, it
wrongly becomes the user's $HOME dir which is not what we want. So check
it is not empty before working with it further.

Signed-off-by: Borislav Petkov <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Steven Rostedt <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/scripts/Makefile.include

@@ -1,3 +1,4 @@
+ifneq ($(O),)
 ifeq ($(origin O), command line)
 	dummy := $(if $(shell test -d $(O) || echo $(O)),$(error O=$(O) does not exist),)
 	ABSOLUTE_O := $(shell cd $(O) ; pwd)
@@ -7,9 +8,10 @@ ifeq ($(objtree),)
 	objtree := $(O)
 endif
 endif
+endif
 
-ifneq ($(OUTPUT),)
 # check that the output directory actually exists
+ifneq ($(OUTPUT),)
 OUTDIR := $(shell cd $(OUTPUT) && /bin/pwd)
 $(if $(OUTDIR),, $(error output directory "$(OUTPUT)" does not exist))
 endif