Enable install target on MacOS

The 'install' program on MacOS does not have the GNU long-form options
nor does it have a -D, so we need to use a separate mkdir -p.
Stop pretending we care about ia64 kernel symbols
Use different path for cscope binary on MacOS

No idea if this is a sensible location for it, but it's where I put it
on this Mac.
Explicitly set hlsearch in .vimrc