[gfortran,patch, RFC] Allow coredump and backtrace on runtime error

[FX Coudert]

> I'm abroad, therefore I can not test this myself. How does your patch
> work with OMP, i.e. multiple threads? Will each thread dump its own
> backtrace? If yes, will they be separable?

 From my experiments, only one thread dumps it backtrace, and it's  
not a full backtrace but only from the point where the thread was  
created:

Backtrace for this error:
   + function gee_.omp_fn.1 (0x400AAC)
     at line 15 of file u.f90
   + /utmp/coudert/gfortran/irun/lib64/libgomp.so.1 [0x2a9570d17c]
   + /lib64/tls/libpthread.so.0 [0x3ff370610a]
   + /lib64/tls/libc.so.6(__clone+0x73) [0x3ff24c5ee3]


We can work later on improving this, but I think it's not so bad a  
behaviour for now.

FX