s390: larl for Simode on 64-bit

[DJ Delorie]

In the TPF case, the software has to explicitly mark such pointers as
SImode (such things happen only when structures that contain addresses
can't change size, for backwards compatibility reasons[1]):

int * __attribute__((mode(SImode))) ptr;

  ptr = &some_var;

so I wouldn't consider this the "default" case for those apps, just
*a* case that needs to be handled "well enough", and the user is
already telling the compiler that they assume those addresses are
32-bit (that either the whole app, or at least the part with that
object, will be linked below 4Gb).

The majority of the addresses are handled as 64-bit.


[1] /me refrains from commenting on the worth of such practices, just
    that they exist and need to be (and have been) supported.