Trouble building a cross compiler for OS development

[Lucas Paul]

Hi all,

I'm trying to update a Nix derivation for GCC so that I can easily and
reliably get a cross compiler for OS development work. In the process of
doing this, I seem to have run into a bit of a roadblock just trying to get
GCC to compile.

I'm more-or-less following a guide:
https://wiki.osdev.org/GCC_Cross-Compiler

My configuration options end up being just slightly different:
--prefix=/nix/store/2qgwg29px8ikpcdy6cn6b66ddxymc1aw-i686-elf-stage-final-gcc-debug-7.4.0
--disable-nls --enable-languages=c\,c++ --without-headers
--build=x86_64-unknown-linux-gnu --host=x86_64-unknown-linux-gnu
--target=i686-elf

I don't think this minor difference should matter. But when I try to
compile, I get an error while configuring libgcc. It claims the
preprocessor isn't sane. Full error and config.log at
https://gist.github.com/Reilithion/02126ee9259d81a54f157e93b3f657d7

I'm no compiler engineer, but it looks to me like the configure script is
using methods for making judgments about the capabilities of the compiler
and preprocessor that will give inaccurate results in case the target
system does not have system headers. And since Nix doesn't keep its system
headers for the host in /usr/include there's no "wrong" headers to fall
back on.

I don't want to be presumptuous, so I invite helpful feedback. But is this
a bug in the configure script?

- Lucas