Merging r299574:

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r299574 | nico | 2017-04-05 14:10:42 -0400 (Wed, 05 Apr 2017) | 17 lines

clang-format: Support formatting utf-8 character literals in C++11+ mode.

clang-format <<END
auto c1 = u8'a';
auto c2 = u'a';
END

Before:
  auto c1 = u8 'a';
  auto c2 = u'a';

Now:
  auto c1 = u8'a';
  auto c2 = u'a';

Patch from Denis Gladkikh <llvm@denis.gladkikh.email>!

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llvm-svn: 301463