Fortran: fix ICE on LOC intrinsic with polymorphic argument [PR125606]

The fix for PR122977 improved the gfc_is_simply_contiguous check for
associate variables, but had a side effect when using the LOC() intrinsic
on SELECT TYPE temporaries where gfc_is_simply_contiguous could return
false.  Fall back to simply taking the address of the variable's address.

	PR fortran/125606

gcc/fortran/ChangeLog:

	* trans-intrinsic.cc (gfc_conv_intrinsic_loc): When the argument
	of LOC() is not scalar or known to be simply contiguous, simply
	take the address of the argument array's first element.

gcc/testsuite/ChangeLog:

	* gfortran.dg/loc_3.f90: New test.