I want to install gcc on Ubuntu 14.04. gcc's dependencies installed fine, but gcc itself doesn't build. I see this error message that I don't understand. Have you seen it before, or can you give me a pointer?

The system has gcc 4.9.2 installed; I am trying to install gcc 5.2 via Spack. This looks as if it was using Spack's binutils package.

Google didn't find any good answers. Apart from "don't mess with your system", there is one message suggesting to build ld with the --with-sysroot option. However, --with-sysroot expects a path as argument, and it's unclear to me what argument that could be. I also don't understand what Spack is trying to achieve by using the --sysroot argument.

configure:4370: checking for C compiler default output file name
configure:4392: /xfs1/eschnetter/src/spack/lib/spack/env/cc    conftest.c  >&5 /xfs1/eschnetter/src/spack/opt/spack/linux-x86_64/gcc-4.9.2/binutils-2.25-gqbrzkvzz2q236u5tkyo7uxn2u5i5b4q/bin/ld: this linker was not configured to use sysroots
collect2: error: ld returned 1 exit status