Dear Fortranners,

the PR rightfully complained that we did not differentiate errors on
ALLOCATE(...,stat=,errmsg=) for failures from allocation of already
allocated objects or insufficient virtual memory.

The attached patch introduces a new STAT value LIBERROR_NO_MEMORY
that is returned for insufficient virtual memory, and a corresponding
(simple and invariant) ERRMSG: "Insufficient virtual memory".

(In the PR Janne mentions checking for errno, but since the standard
malloc(3) only mentions ENOMEM as possible error value, and the user
may replace malloc by a special library, I believe that won't be easy
to handle in a general way.)

Most compilers I tried (Intel/NAG/Crayftn) behave similarly, except
for Nvidia/Flang, which try to return the size of the allocation in
the error message.

I am not sure that this is worth the effort.  First, ERRMSG is very
compiler-dependent anyway and thus not really portable.  If a user
wants to know what the size of the failed allocation is and really
wants to recover, he/she should find that out himself.  Second, I
think that the more important change is the introduction of a STAT
value that allows the distinction between the different causes of
failure.

The testcase should be able to handle 32 and 64 bit systems.
At least that's what I think.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?  Suggestions?

Thanks,
Harald