fix bugs in building.py that is when DefineGroup method's 3rd arges "CPPDEFINES" is not null, then "scons --target=mdk -s" will get errors.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1930 bbd45198-f89e-11dd-88c7-29a3b14d5316

tools/building.py

@@ -261,7 +261,7 @@ def MDK4Project(target, script):
         # get each group's definitions
         if group.has_key('CPPDEFINES') and group['CPPDEFINES']:
             if CPPDEFINES:
-                CPPDEFINES += ';' + group['CPPDEFINES']
+                CPPDEFINES += group['CPPDEFINES']
             else:
                 CPPDEFINES += group['CPPDEFINES']