[flang] Add bind(C) to buitlin C_PTR

[clementval]

Summary

D131585 Adds couple of semantics check for the components of BIND(C)
derived-type. This would raise an error when a component is of C_PTR
type. Add bind(c) to the __builtin_c_ptr type so the wrong error
is not triggered.

[peixin]

LGTM. Checked ifort 2021 iso_c_binding.f90 and it has BIND(C) for both C_PTR and C_FUNPTR.

flang/module/__fortran_builtins.f90

module __Fortran_builtins
 
   intrinsic :: __builtin_c_f_pointer
   intrinsic :: sizeof ! extension
 
   intrinsic :: selected_int_kind
   private :: selected_int_kind
   integer, parameter, private :: int64 = selected_int_kind(18)
 
-  type :: __builtin_c_ptr
+  type, bind(c) :: __builtin_c_ptr
     integer(kind=int64) :: __address
   end type
 
   type, bind(c) :: __builtin_c_funptr
     integer(kind=int64) :: __address
   end type
 
   type :: __builtin_event_type

flang/test/Semantics/bind-c07.f90

+! RUN: bbc -emit-fir -o - %s | FileCheck %s
+
+module bind_c_type
+  use, intrinsic :: iso_c_binding
+
+  type, bind(C) :: t
+    type(c_ptr) :: tcptr = C_NULL_PTR
+  end type
+end module
+
+! CHECK-LABEL: _QMbind_c_typeE.di.t.tcptr