Fortran: fix stack-buffer-overflow passing type to assumed-rank class [PR60576]

Two code paths copied a full GFC_MAX_DIMENSIONS dim[] array from a
descriptor that physically holds only dtype.rank dimensions, triggering
a stack-buffer-overflow detected by AddressSanitizer.

Case 1 - assumed-rank type(T) dummy passed to class(T) assumed-rank:
The caller only allocates storage for dtype.rank dimensions.  The code
generated a static GFC_MAX_DIMENSIONS struct copy of the dim[] array,
reading past the physical end of the descriptor.  Fix by checking
expr->rank == -1 and replacing the static copy with a runtime-sized
__builtin_memcpy of dtype.rank * sizeof(descriptor_dimension) bytes.

Case 2 - fixed-rank type(T) actual passed directly to class(T) assumed-rank:
gfortran uses a rank-specific descriptor type for fixed-rank type arrays
(dim[rank] rather than dim[GFC_MAX_DIMENSIONS]).  The class assumed-rank
formal's descriptor has dim_t[GFC_MAX_DIMENSIONS].  The call to
gfc_class_array_data_assign with lhs_type=true keyed the ARRAY_RANGE_REF
off TREE_TYPE(lhs_dim) = dim_t[GFC_MAX_DIMENSIONS], reading 15*24 = 360
bytes from a descriptor that physically has only rank*24 bytes for the
dim[] array.  Fix by checking CLASS_DATA(fsym)->as->rank == -1 and
passing lhs_type=false so the ARRAY_RANGE_REF is sized by
TREE_TYPE(rhs_dim) = dim_t[rank], copying only the physically present
entries.  Fixed-rank class formals retain lhs_type=true.

Assisted by: Claude Sonnet 4.6

	PR fortran/60576

gcc/fortran/ChangeLog:

	PR fortran/60576
	* trans-array.cc (gfc_conv_array_parameter): For an assumed-rank
	actual argument passed to a CLASS assumed-rank formal, use a
	runtime-sized memcpy for the dim[] entries instead of a full
	GFC_MAX_DIMENSIONS static copy.  For a fixed-rank actual to a
	CLASS assumed-rank formal, pass lhs_type=false to
	gfc_class_array_data_assign so the dim[] copy is sized by the
	RHS descriptor type (dim_t[rank]).  Fixed-rank class formals
	retain lhs_type=true.
	* trans-expr.cc (gfc_conv_derived_to_class): For an assumed-rank
	actual, use a runtime-sized memcpy for the derived_array descriptor
	dim[] copy instead of a full GFC_MAX_DIMENSIONS static copy.

gcc/testsuite/ChangeLog:

	PR fortran/60576
	* gfortran.dg/asan/assumed_rank_26.f90: New test covering both
	assumed-rank and fixed-rank type actuals passed to a CLASS
	assumed-rank dummy.