Fix inconsistent compile condition of two related macros

[EstherWx]

The compile conditions of RAPIDJSON_48BITPOINTER_OPTIMIZATION and RAPIDJSON_64BIT are different. But there will be an error when RAPIDJSON_48BITPOINTER_OPTIMIZATION = 1, RAPIDJSON_64BIT != 1.

Define RAPIDJSON_48BITPOINTER_OPTIMIZATION as RAPIDJSON_64BIT to fix this problem.

Issue: https://github.com/Tencent/rapidjson/issues/2281