tools build: Fix Makefile(s) to properly invoke tools build

Several fixes were needed to allow following builds:
  $ make tools/tmon
  $ make -C <kernelsrc> tools/perf
  $ make -C <kernelsrc>/tools perf

 - some of the tools (perf) use same make variables as in
   kernel build, unsetting srctree and objtree
 - using original $(O) for O variable
 - perf build does not follow the descend function setup
   invoking it via it's own make rule

I tried the rest of the tools/Makefile targets and they
seem to work now.

Reported-by: Brian Norris <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Norris <[email protected]>
Cc: David Ahern <[email protected]>
Cc: David Howells <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

0 files changed, 0 insertions, 0 deletions