perf tools: Allow specifying O= to build files in a separate directory

Avoiding polluting the source tree with build files.
Reported-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/PERF-VERSION-GEN

 #!/bin/sh
 
-GVF=PERF-VERSION-FILE
+if [ $# -eq 1 ]  ; then
+	OUTPUT=$1
+fi
+
+GVF=${OUTPUT}PERF-VERSION-FILE
 DEF_VER=v0.0.2.PERF
 
 LF='