6800154: Add comments to long_by_long_mulhi() for better understandability Summary: This patch adds a comment pointing to the Hacker's Delight version of the algorithm plus a verbatim copy of it. Furthermore it adds inline comments. Reviewed-by: kvn, jrose

^build/
^dist/
^nbproject/private/
^src/share/tools/hsdis/bin/
^src/share/tools/IdealGraphVisualizer/[a-zA-Z0-9]*/build/
^src/share/tools/IdealGraphVisualizer/build/
^src/share/tools/IdealGraphVisualizer/dist/