Windows: Compile with /utf-8 flag

Add /utf-8 flag to compilation on MSVC. This flag makes sure that source files
and static strings included in the application are UTF-8 strings.

src/CMakeLists.txt

@@ -150,7 +150,7 @@ endif()
 
 if(MSVC)
   # TODO: Find a way to do this cleanly for non MSVC users.
-  set(SM_COMPILE_FLAGS "${SM_COMPILE_FLAGS} /MP2")
+  set(SM_COMPILE_FLAGS "${SM_COMPILE_FLAGS} /MP2 /utf-8")
 endif()
 
 set_target_properties("${SM_EXE_NAME}"