change the SConstruct in ls1bdev in order to use the rt-thread eclipse wizard

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1925 bbd45198-f89e-11dd-88c7-29a3b14d5316

bsp/ls1bdev/SConstruct

@@ -2,7 +2,10 @@ import os
 import sys
 import rtconfig
 
-RTT_ROOT = os.path.normpath(os.getcwd() + '/../..')
+if os.getenv('RTT_ROOT'):
+    RTT_ROOT = os.getenv('RTT_ROOT')
+else:
+    RTT_ROOT = os.path.normpath(os.getcwd() + '/../..')
 sys.path = sys.path + [os.path.join(RTT_ROOT, 'tools')]
 from building import *