compiler: fix missing case in Array_type::get_value_pointer

    
    Update the code in Array_type::get_value_pointer that handles
    "lvalue" context to look for both regular var expressions
    and temp var expressions, since both can appear in array/slice
    index expressions on the left hand side of assignments.
    
    Reviewed-on: https://go-review.googlesource.com/46170

From-SVN: r249486

gcc/go/gofrontend/MERGE

-a4b455aa584e0d6e362a88597f11bba1427088e2
+0b93af68feb0a4135e83dd9e6c11df1563d862a9
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/types.cc

@@ -7635,12 +7635,19 @@ Array_type::get_value_pointer(Gogo*, Expression* array, bool is_lvalue) const
     {
       Temporary_reference_expression* tref =
           array->temporary_reference_expression();
+      Var_expression* ve = array->var_expression();
       if (tref != NULL)
         {
           tref = tref->copy()->temporary_reference_expression();
           tref->set_is_lvalue();
           array = tref;
         }
+      else if (ve != NULL)
+        {
+          ve = new Var_expression(ve->named_object(), ve->location());
+          ve->set_in_lvalue_pos();
+          array = ve;
+        }
     }
 
   return Expression::make_slice_info(array,