PR95331 - Unlimited polymorphic arrays have wrong bounds.

PR95331 - Unlimited polymorphic arrays have wrong bounds.

When iterating over a class array use the bounds provided by the
transformed descriptor (in sym->backend_decl) instead of the original
bounds of the array (in the descriptor passed in the class _data)
which are passed in se->expr.

The patch partially depends on the patch for PR52351 and PR85868, but
does not seems to break anything by itself.

gcc/fortran/ChangeLog:

2020-06-11  José Rui Faustino de Sousa  <jrfsousa@gmail.com>

	PR fortran/95331
	* trans-array.c (gfc_conv_array_ref): For class array dummy
	arguments use the transformed descriptor in sym->backend_decl
	instead of the original descriptor.

gcc/testsuite/ChangeLog:

2020-06-11  José Rui Faustino de Sousa  <jrfsousa@gmail.com>

	PR fortran/95331
	* gfortran.dg/PR95331.f90: New test.