Fortran: Cray pointer comparison wrongly optimized away [PR106692]

	PR fortran/106692

gcc/fortran/ChangeLog:

	* trans-expr.cc (gfc_conv_expr_op): Inhibit excessive optimization
	of Cray pointers by treating them as volatile in comparisons.

gcc/testsuite/ChangeLog:

	* gfortran.dg/cray_pointers_13.f90: New test.