perf tools: Make clean leaves some files

Use LIB_OBJS and BUILTIN_OBJS for .o files.

LIB_FILE is already prefixed with OUTPUT.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110807083932.9C0E514C03B@msa103.auone-net.jp
Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>