Bind(C): Correct sizes of some types in CFI_establish

Bind(C): Correct sizes of some types in CFI_establish

CFI_establish was failing to set the default elem_len correctly for
CFI_type_cptr, CFI_type_cfunptr, CFI_type_long_double, and
CFI_type_long_double_Complex.

2021-07-13  Sandra Loosemore  <sandra@codesourcery.com>

libgfortran/
	PR libfortran/101305
	* runtime/ISO_Fortran_binding.c (CFI_establish): Special-case
	CFI_type_cptr and CFI_type_cfunptr.  Correct size of long double
	on targets where it has kind 10.