Summary:
There is a switch for choosing the right concatinator for concating js file together
in `lib/InternalBytecode/CMakeLists.txt`. When crosscompiling (eg compiling Android on Windows)
it chooses the target platform (not WIN32) despite being launched on Windows.
CMAKE_HOST_WIN32 var is suggested to be used instead to make the proper detection.
Pull Request resolved: https://github.com/facebook/hermes/pull/527
Test Plan:
Environment: Win10, Powershell
1. cd one folder up from hermes repo
2. Configure host build `python3 hermes/utils/build/configure.py --build-system='Visual Studio 15 2017' ./build`
3. Run the host build `MSBuild.exe ALL_BUILD.vcxproj /p:Configuration=Debug`
4. Set HERMES_WS_DIR: `$env:HERMES_WS_DIR=<path to build foder>`
5. `cd hermes\android; ./gradlew assembleNoIntl`
6. Actual result: the following error
```
FAILED: cmd.exe /C "cd /D [..]hermes\lib\InternalBytecode && cat [..]\hermes\lib\InternalBytecode\00-header.js [..]hermes\lib\InternalBytecode\01-Promise.js [..]hermes\lib\InternalBytecode\02-AsyncFn.js [..]hermes\lib\InternalBytecode\99-footer.js > [..]staging/hermes/cmake/nointlDebug/armeabi-v7a/lib/InternalBytecode/InternalBytecode.js"
'cat' is not recognized as an internal or external command,
```
7. Expected result: BUILD SUCCESSFUL
Reviewed By: neildhar
Differential Revision: D29005361
Pulled By: Huxpro
fbshipit-source-id: 5ead4c1c4869f076db20c0ea9c6bb2fa775ae8b5
645b08e574