Clean up the Feature and Regression test output to (a) use section headers,

Clean up the Feature and Regression test output to (a) use section headers,
(b) avoid <pre> tag so page width doesn't become excessive, (c) omit the
execution time stats, (d) format each reported test in a list with bold
headings for readability, (e) omit long lines of dashes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13912 91177308-0d34-0410-b5e6-96231b3b80d8