Just /source-charset:utf-8 didn't work. Try /utf-8.

Change-Id: I90862237f38c70a04e16c96ce67bab11bf61718b
Reviewed-on: https://code-review.googlesource.com/21431
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 09a8bb8..f87c4ff 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,7 +35,7 @@
   add_compile_options(/wd4100 /wd4201 /wd4456 /wd4457 /wd4702 /wd4815)
   # Without a byte order mark (BOM), Visual Studio assumes that the source
   # file is encoded using the current user code page, so we specify UTF-8.
-  add_compile_options(/source-charset:utf-8)
+  add_compile_options(/utf-8)
 elseif(CYGWIN OR MINGW)
   # See https://stackoverflow.com/questions/38139631 for details.
   add_compile_options(-std=gnu++11)