[Ada] Fix indentation in generated AST construction functions

[Pierre-Marie de Rodat via Gcc-patches]

In the generated nmake.adb file the "return" keyword in function
declarations was printed at the start of a line. Now it is correctly
indented, which makes the generated code easier to read.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * gen_il-gen.adb (Put_Make_Spec): Don't emit the LF character in
        the middle of a string, because the Put routine won't indent it
        properly.
diff --git a/gcc/ada/gen_il-gen.adb b/gcc/ada/gen_il-gen.adb
--- a/gcc/ada/gen_il-gen.adb
+++ b/gcc/ada/gen_il-gen.adb
@@ -2423,7 +2423,8 @@ package body Gen_IL.Gen is
             end if;
          end loop;
 
-         Put (S, ")" & LF & "return " & Node_Or_Entity (Root) & "_Id");
+         Put (S, ")" & LF);
+         Put (S, "return " & Node_Or_Entity (Root) & "_Id");
          Decrease_Indent (S, 2);
          Decrease_Indent (S, 1);
       end Put_Make_Spec;