perf beauty mmap_flags: Conditionaly define the mmap flags

So that in older systems we get it in the mmap flags scnprintf routines:

  $ tools/perf/trace/beauty/mmap_flags.sh  | head -9 2> /dev/null
  static const char *mmap_flags[] = {
  	[ilog2(0x40) + 1] = "32BIT",
  #ifndef MAP_32BIT
  #define MAP_32BIT 0x40
  #endif
  	[ilog2(0x01) + 1] = "SHARED",
  #ifndef MAP_SHARED
  #define MAP_SHARED 0x01
  #endif
  $

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>