do not use iso_c_binding

Author: perazz

src/stdlib_string_type.fypp

@@ -17,7 +17,6 @@ module stdlib_string_type
        & to_title_ => to_title, to_sentence_ => to_sentence, reverse_ => reverse
     use stdlib_kinds, only : int8, int16, int32, int64, lk, c_bool
     use stdlib_optval, only: optval
-    use iso_c_binding, only: c_loc,c_associated
     implicit none
     private
 
@@ -682,8 +681,10 @@ contains
     elemental subroutine move_string_string(from, to)
         type(string_type), intent(inout), target :: from
         type(string_type), intent(inout), target :: to
+        type(string_type), pointer :: fromp
 
-        if (c_associated(c_loc(from),c_loc(to))) return
+        fromp => from
+        if (associated(fromp,to)) return
         call move_alloc(from%raw, to%raw)
 
     end subroutine move_string_string