cmake : fix MSVC compile error C3688 on non-unicode Windows (#1110)

CMakeLists.txt

@@ -240,6 +240,7 @@ if (${CMAKE_SYSTEM_PROCESSOR} MATCHES "arm" OR ${CMAKE_SYSTEM_PROCESSOR} MATCHES
 else()
     message(STATUS "x86 detected")
     if (MSVC)
+            add_compile_options(/utf-8)
             if(NOT WHISPER_NO_AVX2)
                 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /arch:AVX2")
                 set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} /arch:AVX2")