WIN32 vs _WIN32 compat. fixes

 _WIN32` is predefined ("Always defined" per the documentation) whereas `WIN32` isn't - according to the documentation: https://msdn.microsoft.com/en-us/library/b0084kay.aspx

Change-Id: I344a874fb97ddbd2c1d8722878184d63d65fab76
Reviewed-on: https://code-review.googlesource.com/3010
Reviewed-by: Paul Wankadia <junyer@google.com>
4 files changed