TS-2168: Use #ifdef to control reclaimable freelist options

1) Define reclaimabe freelist options only when compiles ATS
   with --enable-reclaimabe-freelist,

2) "proxy.config.allocator.enable_reclaim" will be set to 1 in
   RecordsConfig.cc by default for two reason:
   a) it should keep consistent with records.config.default.in
      when enable reclaimable freelist, and
   b) more important, most users want to get reclaim feature when
      they compiles ATS with --enable-reclaimable-freelist.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>