OpenMP/Fortran: Fix allocatable-component mapping of derived-type array comps

OpenMP/Fortran: Fix allocatable-component mapping of derived-type array comps

The check whether the location expression in map clause has allocatable
components was failing for some derived-type array expressions such as
  map(var%tiles(1))
as the compiler produced
  _4 = var.tiles;
  MEMREF(_4, _5);
This commit now also handles this case.

gcc/fortran/ChangeLog:

	* trans-openmp.cc (gfc_omp_deep_mapping_do): Handle SSA_NAME if
	a def_stmt is available.

libgomp/ChangeLog:

	* testsuite/libgomp.fortran/alloc-comp-4.f90: New test.