SCons: allow set object files in DefineGroup

The source files can be the raw file names end with .c or .o. So return
the raw file names is more flexible than wrap them with Object.

tools/building.py

@@ -364,9 +364,10 @@ def DefineGroup(name, src, depend, **parameters):
     if group.has_key('LIBPATH'):
         Env.Append(LIBPATH = group['LIBPATH'])
 
-    objs = Env.Object(group['src'])
     if group.has_key('LIBRARY'):
-        objs = Env.Library(name, objs)
+        objs = Env.Library(name, group['src'])
+    else:
+        objs = group['src']
 
     # merge group 
     for g in Projects: