llvm-build: Don't write out the required_libraries list for "special" components, it is generated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146435 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/llvm-build/llvmbuild/main.py b/utils/llvm-build/llvmbuild/main.py
index 71e11d7..550c740 100644
--- a/utils/llvm-build/llvmbuild/main.py
+++ b/utils/llvm-build/llvmbuild/main.py
@@ -666,6 +666,7 @@
             fatal("special component %r must have empty %r list" % (
                     name, 'add_to_library_groups'))
 
+        info._is_special_group = True
         return info
 
     info_map = dict((ci.name, ci) for ci in project.component_infos)