[Driver] Bring back "Clean up Debian multiarch /usr/include/<triplet> madness"...

[Driver] Bring back "Clean up Debian multiarch /usr/include/<triplet> madness" and restore i586-linux-gnu

This reverts commit 933d146f and 21b211a8
(which mis-identified the issue) but restores i586-linux-gnu which was
removed by `Gnu.cpp: remove obsoleted i386 triple detection from end-of-life distribution versions`.

Looks like i586-linux-gnu was not dead enough (used in a sysroot by Fuchsia build bot based on Debian jessie:)
but i486-linux-gnu should be very dead by now.