scons: Explicit the config option HAVE_DEPRECATED_NAMESPACE type bool

Currently the type of HAVE_DEPRECATED_NAMESPACE is used to detect
if the compiler support gnu::deprecated feature. The return type
of conf.TryCompile is int, but HAVE_DEPRECATED_NAMESPACE is used
as boolean type. The CL is add bool type caster to ensure the type
of it is boolean.

Change-Id: Ife7d9716e485a8be8722d58776f064e7c2268a30

src/base/SConsopts

@@ -69,11 +69,13 @@ werror_env.Append(CCFLAGS=['-Werror'])
 with gem5_scons.Configure(werror_env) as conf:
 
     # Store result in the main environment
-    main['CONF']['HAVE_DEPRECATED_NAMESPACE'] = conf.TryCompile('''
-        int main() {return 0;}
-        namespace [[gnu::deprecated("Test namespace deprecation")]]
-        test_deprecated_namespace {}
-    ''', '.cc')
+    main['CONF']['HAVE_DEPRECATED_NAMESPACE'] = bool(
+        conf.TryCompile('''
+            int main() {return 0;}
+            namespace [[gnu::deprecated("Test namespace deprecation")]]
+            test_deprecated_namespace {}
+        ''', '.cc')
+    )
 
     if not main['CONF']['HAVE_DEPRECATED_NAMESPACE']:
         warning("Deprecated namespaces are not supported by this compiler.\n"