[mkroot] [landley/mkroot] Smoke test the correct compiler (#6)

[Rob Landley]

On 06/13/2017 05:06 PM, Rob Landley wrote:
> That said, the toybox airlock build we do is dynamic linking (or at
> least leaving it to the host toolchain to determine how to link the
> binaries), so I don't strictly have to _require_ static linking. I can
> either move this check into the "native compiling" if/else, change it to
> just check that it can build a runnable hello world program, or remove
> it entirely.

The problem with moving it is it's currently run right after the paths
are set (including the output directory to drop the hello world binary
in), which have to be after we check whether or not we're cross compiling.

I'd rather not split the path variable setting into two blocks, so I'll
just make the check a warning in the cross compiling case, and only be
an error in the native compiling case. I'll also clarify the error
message that the HOST compiler can't produce static binaries (which is a
common issue because Red Hat broke theirs).

Providing a broken target toolchain is still pilot error. There are way
too many things that could go wrong there for me to check them all.

Rob