Cause the various warnings list to be generated via a <ul> list with

Cause the various warnings list to be generated via a <ul> list with
text enclosed in <tt>. This ensures that (a) the text is in a fixed width
font (to indicated generated text) and (b) the text wraps without causing
the page width to be extended. The main result of this is that the report
will wrap to conform to the window size in which it is displayed instead of
having a very wide length if a warning message is long.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26916 91177308-0d34-0410-b5e6-96231b3b80d8