compiler: set varargs lowered for imported call expressions

    
    Fix compiler buglet: varargs lowering happens before inlinable
    function bodies are written out to export data, so set the "varargs
    lowered" flag on call expressions that we import.
    
    Fixes golang/go#32922
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/184919

From-SVN: r273026

gcc/go/gofrontend/MERGE

-ae7d7e05bce19aefaa27efe2ee797933aafbef06
+bf66d40bc7adb438dcfac85d73bfa7b17217eed9
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/expressions.cc

@@ -18338,6 +18338,7 @@ Expression::import_expression(Import_expression* imp, Location loc)
 	    }
 	  imp->require_c_string(")");
 	  expr = Expression::make_call(expr, args, is_varargs, loc);
+          expr->call_expression()->set_varargs_are_lowered();
 	}
       else if (imp->match_c_string("["))
 	{
@@ -19389,4 +19390,3 @@ Numeric_constant::hash(unsigned int seed) const
 
   return (static_cast<unsigned int>(val) + seed) * PRIME;
 }
-