llvm-cov: Added -a option for block data.

Similar to gcov, llvm-cov will now print out the block count at the end
of each block. Multiple blocks can end on the same line.

One computational difference is by using -a, llvm-cov will no longer
simply add the block counts together to form a line count. Instead, it
will take the maximum of the block counts on that line. This has a
similar effect to what gcov does, but generates more correct counts in
certain scenarios.

Also updated tests.

llvm-svn: 196856