#589 Consider adding installation support

[Joseph Koshy]

Support installing Elftoolchain artefacts after building.

This would involve one or more of:

• Verifying that DESTDIR= support works correctly on all our target platforms.
• Renaming libraries and binaries so as not to clash with existing binaries and libraries on the user's system.
• Adapting install locations in some system-specific manner.
• Preparing packaging instructions for our supported platforms (Ports, Pkgsrc, Debian packages, etc).