tools/perf: Clean up util/include/linux/compiler.h

Use the standard CPP style we use in the kernel:

 #ifndef foo
 # define foo bar
 #endif

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-iqyVrrHqpn0eiwenvgwrh8lf@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>