clang-format: Fix space in decltype-constexprs.

Before:
  static constexpr bool Bar = decltype(bar()) ::value;

After:
  static constexpr bool Bar = decltype(bar())::value;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189449 91177308-0d34-0410-b5e6-96231b3b80d8