Our implementation of the stack probe requires the probe interval to
be used as displacement in an address operand.  The maximum probe
interval currently is 64k.  This would exceed short displacements.
Trim that value down to 4k if that happens.  This might result in too
many probes being generated only on the oldest supported machine level
z900.

gcc/ChangeLog:

2018-08-09  Andreas Krebbel  <krebbel@linux.ibm.com>

	PR target/84332
	* config/s390/s390.c (s390_option_override_internal): Reduce the
	stack-clash-protection-probe-interval param if it would be too big
	for z900.

gcc/testsuite/ChangeLog:

2018-08-09  Andreas Krebbel  <krebbel@linux.ibm.com>

	PR target/84332
	* gcc.target/s390/pr84332.c: New testcase.

From-SVN: r263441