fortran: Generate an array temporary reference [PR102043]

fortran: Generate an array temporary reference [PR102043]

This avoids regressing on char_cast_1.f90 and char_cast_2.f90 later in
the patch series when the code generation for array references is
changed to use pointer arithmetic.

The regressing testcases match part of an array reference in the
generated tree dump and it’s not clear how the pattern should be
rewritten to match the equivalent with pointer arithmetic.

This change uses a method specific to array temporaries to generate
array-references, so that these array references are flagged as safe
for array indexing and will not be updated to use pointer arithmetic.

	PR fortran/102043

gcc/fortran/ChangeLog:
	* trans-array.cc (gfc_conv_expr_descriptor): Use
	gfc_conv_tmp_array_ref.