Could not find <hash_map>

[ZengruiWang]

Hi, I am building protobuf-emscripten using Visual Studio from this repo, but it shows me the error message:
1>C:\Users\Ray\Documents\GitHub\protobuf-emscripten\src\google\protobuf\stubs\hash.h(43,10): fatal error : 'hash_map' file not found
1> #include HASH_MAP_H
1> ^
1> C:\Users\Ray\Documents\GitHub\protobuf-emscripten\vsprojects\config.h(5,20): note: expanded from macro 'HASH_MAP_H'
1> #define HASH_MAP_H <hash_map>
1> ^
1> 1 error generated.

I am sure Emscripten has hash_map but why it can't find it?

Thank you!