Making PROG_PREFIX a symlink option

Arch Linux and Debian current package uutils differently:

• Arch Linux installs them to /usr/bin/uu-* using PROG_PREFIX
• Debian installs them to /usr/lib/cargo/bin/coreutils/ using BINDIR

The Debian approach has the benefit of allowing to edit $PATH to opt-into uutils. I wonder if, as a compromise, there could be a way to combine those two, so:

• there's a folder that can be added to $PATH
• the binaries are also symlinked from that folder to /usr/bin with a uu-* prefix so there's no breaking change

This could look like:

• PREFIX=/usr
• BINDIR=/usr/lib/cargo/bin
• SYMLINKDIR=/usr/bin
• PROG_PRFIX=uu-

This would install sort to:

• /usr/lib/cargo/bin/sort
• /usr/bin/uu-sort

There's currently users trying to build work-arounds (both of them removing system coreutils, risking their system becoming unbootable):

• https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=coreutils-uutils-symlink
• https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=coreutils-uutils

Start by tracing how PROG_PREFIX and BINDIR control installation and where command-line binaries are placed. Define the SYMLINKDIR behavior described in the issue, preserving the existing uu-* paths while also installing unprefixed binaries in the PATH-addable directory; done means both locations are supported without removing system coreutils.