embedding_wrapper.c: Fix Unicode arguments in Windows

[raphasampaio]

Based on https://github.com/JuliaLang/julia/blob/873a1e41a2dd84276b6ef6a3a47c452850808c50/cli/Makefile#L14 and https://github.com/JuliaLang/julia/blob/69fcb5745bda8a5588c089f7b65831787cffc366/ui/repl.c#L201

close #835

[DilumAluthge]

Would it be possible to add a test?

[raphasampaio]

Sure @DilumAluthge

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.76%. Comparing base (9bef815) to head (127c545).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1008      +/-   ##
==========================================
+ Coverage   87.73%   87.76%   +0.03%     
==========================================
  Files           3        3              
  Lines         799      801       +2     
==========================================
+ Hits          701      703       +2     
  Misses         98       98              

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