Better trade-off for excess characters vs. staying within the column limits.

When we break a long line like:
Column limit: 21
                      |
  // foo foo foo foo foo foo foo foo foo foo foo foo

The local decision when to allow protruding vs. breaking can lead to this
outcome (2 excess characters, 2 breaks):
  // foo foo foo foo foo
  // foo foo foo foo foo
  // foo foo

While strictly staying within the column limit leads to this strictly better
outcome (fully below the column limit, 2 breaks):
  // foo foo foo foo
  // foo foo foo foo
  // foo foo foo foo

To get an optimal solution, we would need to consider all combinations of excess
characters vs. breaking for all lines, but that would lead to a significant
increase in the search space of the algorithm for little gain.

Instead, we blindly try both approches and·select the one that leads to the
overall lower penalty.

Differential Revision: https://reviews.llvm.org/D40605

llvm-svn: 319541

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