[libgfortran,patch] Add compiler check when configuring libgfortran

[Eric Botcazou]

> Attached patch fixes a long-standing bug in libgfortran configury by
> adding an explicit check that we have a working gfortran compiler, and
> otherwise error out.

Thanks for tackling this!

> Without this patch, a miscompiled (or mislinked) gfortran will only induce
> an error late in the libgfortran build, and with a very cryptic error
> message (see PR 26893 for details). With this patch, a non usable compiler
> will yield the following error message:
>
> checking whether the GNU Fortran compiler is working... no
> configure: error: GNU Fortran is not working; please report a bug in
> http://gcc.gnu.org/bugzilla, attaching
> /home/fxcoudert/svn/debug3/ibin/i686-pc-linux-gnu/libgfortran/config.log

Perhaps we can tell the user to first look into the failure?  The error 
message could mention a few hints about GMP and MFPR too.

> Bootstrapped and tested on i686-linux. OK for mainline? Would it be OK
> to backport this to 4.2, a few weeks after it has been commited to
> mainline? (I think it's an annoying bug for users compiling on unusual
> platforms or using unusual configurations).

unusual == non-Linux I presume?  Solaris is definitely not unusual.
I'd second putting this on the 4.2 branch, rather sooner than later.

-- 
Eric Botcazou