I grabbed the source out of the Slackware tree instead (isl-0.24).
Just a heads-up: there's a bug in the build script. The target CFLAGS and CXXFLAGS should NOT be set to the host flags. This may still work for a 64-bit machine but will fail for a 32-bit machine.
I emailed the maintainer last week about this but haven't heard back.
See
this commit.
There's a newer version of the avr-libc just released too that build fine on 15.0.