[formatv] Add the ability to specify a fill character when aligning.

Previously if you used fmt_align(7, Center) you would get the
output '   7   '.  It may be desirable for the user to specify
the fill character though, for example producing '---7---'.  This
patch adds that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305449 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed