clang/unittests/Format/FormatTest.cpp: Suppress utf8 literals with _MSC_VER. MS cl.exe is unaware of BOM-less utf8 source files.

FIXME: Encode Cyrillic and CJK characters below to appease MS compilers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183366 91177308-0d34-0410-b5e6-96231b3b80d8