t/sdl_test: Compile as UTF-8
Fix the following warning:
sdl_program.cpp(25): warning C4566: character represented by universal-character-name '\u2603' cannot be represented in the current code page (1252)
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Fix the following warning:
sdl_program.cpp(25): warning C4566: character represented by universal-character-name '\u2603' cannot be represented in the current code page (1252)