Include new projects: build, buildroot, prebuilts

kvm-master branch was created in buildroot as master is used by the
upstream project.
diff --git a/default.xml b/default.xml
index 01f61b5..1a1ea57 100644
--- a/default.xml
+++ b/default.xml
@@ -3,8 +3,11 @@
   <remote name="origin" fetch=".." />
   <default remote="origin" revision="master" />
 
+  <project path="build" name="build" />
+  <project path="buildroot" name="buildroot" revision="kvm-master" />
   <project path="kvmtool" name="kvmtool" />
   <project path="kvm-unit-tests" name="kvm-unit-tests" />
   <project path="linux" name="linux" />
   <project path="misc" name="misc" />
+  <project path="prebuilts" name="prebuilts" />
 </manifest>