Initial support for multiple variable declarations.

Before:
  SomeType aaaaaaaaaaaaaaaaa = aaaaaa->aaaaaaaaaaaaaaaaa(),
      aaaaaaaaaaa = aaaaaa->aaaaaaaaaaa();
After:
  SomeType aaaaaaaaaaaaaaaaa = aaaaaa->aaaaaaaaaaaaaaaaa(),
           aaaaaaaaaaa = aaaaaa->aaaaaaaaaaa();

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173792 91177308-0d34-0410-b5e6-96231b3b80d8