Use more memory than default c++

[xiaohunqupo]

In my project, test result like this
tcmalloc Release/Debug work1 Memory CommitSize Work2 Memory CommitSize
N D 28s 409MB 935MB 1m20s 3581MB 5211MB
Y D 23s 475MB 1053MB 1m11s 4083MB 5653MB
N R 18S 416MB 967MB 22s 3652MB 5295MB
Y R 18S 506MB 1049MB 20s 4140MB 5650MB

[ckennelly]

TCMalloc caches memory to improve CPU performance. This may not always be optimal for all environments, especially memory-constrained ones.