[RFC, patch] Detect lack of 32-bit devel environment on x86_64-linux targets

[FX <fxcoudert at gmail dot com>]

Given that I did not receive any feedback on my earlier email on this topic, I would like to send this patch for RFC. I'm not expert at this configury-stuff, so please try to comment on both the test proposed and my actual implementation :)

The idea is to find a patch which both catches probable issues early on for most x86_64-linux users, yet does not make build more complex for our power users. So, I propose to include a specific check in toplevel configure:

The cumulative conditions I suggest, in order to make it as unobtrusive as possible for current users, are:

 1. if we build a native compiler,
 2. on x86_64-linux (and possible other x86_64 targets whose maintainers want to opt in),
 3. and neither --enable-multilib nor --disable-multilib were passed

then:

 a. we check that the native compiler can handle 32-bit, by compiling a test executable with the "-m32" option
 b. if we fail, we error out of the configure process, indicating that this can be overriden with --{enable,disable}-multilib

I suspect this might catch (at configure time) the large majority of users who currently get stuck at stage 2 with the "gnu/stubs-32.h" error, while being invisible to a large majority of the power users.

So, what do you think?

FX

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