give tools/build its own group

Change-Id: I5151c4feafd25689d94342b0a3d7ca269ecb34ec
diff --git a/default.xml b/default.xml
index cb6dba2..6590aad 100644
--- a/default.xml
+++ b/default.xml
@@ -312,7 +312,7 @@
   <project path="system/netd" name="platform/system/netd" />
   <project path="system/security" name="platform/system/security" />
   <project path="system/vold" name="platform/system/vold" />
-  <project path="tools/build" name="platform/tools/build" />
+  <project path="tools/build" name="platform/tools/build" groups="toolsbuild" />
   <project path="tools/motodev" name="platform/tools/motodev" />
 
 </manifest>