Improve handling of comments in static initializers.

Also adding more tests.

We can now keep the formatting of something like:

static SomeType type = { aaaaaaaaaaaaaaaaaaaa, /* comment */
                         aaaaaaaaaaaaaaaaaaaa /* comment */,
                         /* comment */ aaaaaaaaaaaaaaaaaaaa,
                         aaaaaaaaaaaaaaaaaaaa, // comment
                         aaaaaaaaaaaaaaaaaaaa };

Note that the comment in the first line is handled like a trailing line comment
as that is likely what the user intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172711 91177308-0d34-0410-b5e6-96231b3b80d8