Add UTF-8 encoding support in setup.cmake for MSVC (PR #415)

The source files are all encoded by UTF-8 without BOM. This will raise
warnings and errors when compiling by the MSVC with some active code
pages (ACP). The file `test/ask.cxx` contains such characters with UTF-8
encoding. Adding `/utf-8` here is equivalent to specifying
`/source-charset:utf-8 /execution-charset:utf-8`, and all warnings and
errors are removed.

CMake/setup.cmake

@@ -116,6 +116,7 @@ if (WIN32)
   if (MSVC)
     add_definitions (-DWIN32_LEAN_AND_MEAN)
     add_definitions (-D_CRT_SECURE_NO_WARNINGS)
+    add_compile_options (/utf-8)  # This is equivalent to specifying `/source-charset:utf-8 /execution-charset:utf-8`
     set (BORDER_WIDTH 2)
   endif (MSVC)
   if (CMAKE_C_COMPILER_ID STREQUAL GNU)