clang-format: Allow "single column" list layout even if that violates the

column limit.

Single-column layout basically means that we format the list with one
element per line. Not doing that when there is a column limit violation
doesn't change the fact that there is an item that doesn't fit within
the column limit.

Before (with a column limit of 30):
  std::vector<int> a = {
      aaaaaaaa, aaaaaaaa,
      aaaaaaaa, aaaaaaaa,
      aaaaaaaaaa, aaaaaaaa,
      aaaaaaaaaaaaaaaaaaaaaaaaaaa};

After:
  std::vector<int> a = {
      aaaaaaaa,
      aaaaaaaa,
      aaaaaaaa,
      aaaaaaaa,
      aaaaaaaaaa,
      aaaaaaaa,
      aaaaaaaaaaaaaaaaaaaaaaaaaaa};

(and previously we would have formatted like "After" it wasn't for the one
item that is too long)

llvm-svn: 290084