base: Cleanup Debug::CompoundFlag

Compound flags are currently constructed using a constructor with a
finite set of arguments that default to nullptr that refer to child
flags. C++11 introduces two cleaner ways to achieve the same thing,
variadic templates and initializer_list. Use an initializer list to
pass dependent flags.

Change-Id: Iadcd04986ab20efccfae9b92b26c079b9612262e
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34115
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/SConscript

@@ -1071,15 +1071,12 @@ namespace Debug {
         if not compound:
             code('SimpleFlag $name("$name", "$desc");')
         else:
-            comp_code('CompoundFlag $name("$name", "$desc",')
+            comp_code('CompoundFlag $name("$name", "$desc", {')
             comp_code.indent()
-            last = len(compound) - 1
-            for i,flag in enumerate(compound):
-                if i != last:
-                    comp_code('&$flag,')
-                else:
-                    comp_code('&$flag);')
+            for flag in compound:
+                comp_code('&$flag,')
             comp_code.dedent()
+            comp_code('});')
 
     code.append(comp_code)
     code()