clang-format: Don't remove existing spaces between identifier and ::.

This can lead to bad behavior with macros that are used to annotate
functions (e.g. ALWAYS_INLINE).

Before, this:
  ALWAYS_INLINE ::std::string getName() ...

was turned into:
  ALWAYS_INLINE::std::string getName() ...

If it turns out that clang-format is failing to clean up a lot of the
existing spaces now, we can add more analyses of the identifier. It
should not currently. Cases where clang-format breaks nested name
specifiers should be fine as clang-format wraps after the "::". Thus, a
line getting longer and then shorter again should lead to the same
original code.

llvm-svn: 295437