scons: New build= option, with support for checked builds.

Where checked build is compiler optimizations plus debugging checks --
ideal for testing CPU bound loads and running test automation loads.
diff --git a/scons/wcesdk.py b/scons/wcesdk.py
index bf73c2d..e82f255 100644
--- a/scons/wcesdk.py
+++ b/scons/wcesdk.py
@@ -122,7 +122,7 @@
     host_cpu = os.environ.get('_HOSTCPUTYPE', 'i386')
     target_cpu = os.environ.get('_TGTCPU', 'x86')
 
-    if env['debug']:
+    if env['build'] == 'debug':
         build = 'debug'
     else:
         build = 'retail'