fix allocator related compile error on wp8/8.1 and winrt

AllocatorTest will crash on WP8 and WP8.1 simulator, the error information:
stop at AllocatorTest.cpp line 97
0x76EA277C 处(位于 TaskHost.exe 中)最可能的异常: Microsoft C++ 异常: std::bad_alloc，位于内存位置 0x0194EC70 处。
0x76EA277C 处(位于 TaskHost.exe 中)有未经处理的异常: Microsoft C++ 异常: std::bad_alloc，位于内存位置 0x0194EC70 处。

This maybe due to the KNumberOfInstances(100000) is too large.