update macro definition for windows

[wbpcode]

MSVC has predefined macro _WIN32

check: https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=msvc-160

The pr mainly made the following changes:

• update some macro definition for windows build.
• fix the bug of encoding error when the string length exceeds 2*32768.

Signed-off-by: wbpcode comems@msn.com

[wbpcode]

I think it is ready for a review @zyfjeff I hope you can take a look at it when you have free time, thank you. 😄

[zyfjeff]

LGTM