LLVMBuild: Introduce a common section which currently has a list of the
subdirectories to traverse into.
 - Originally I wanted to avoid this and just autoscan, but this has one key
   flaw in that new subdirectories can not automatically trigger a rerun of the
   llvm-build tool. This is particularly a pain when switching back and forth
   between trees where one has added a subdirectory, as the dependencies will
   tend to be wrong. This will also eliminates FIXME implicitly.

llvm-svn: 146436
diff --git a/llvm/lib/CodeGen/LLVMBuild.txt b/llvm/lib/CodeGen/LLVMBuild.txt
index 60334c6..fee0347 100644
--- a/llvm/lib/CodeGen/LLVMBuild.txt
+++ b/llvm/lib/CodeGen/LLVMBuild.txt
@@ -15,6 +15,9 @@
 ;
 ;===------------------------------------------------------------------------===;
 
+[common]
+subdirectories = AsmPrinter SelectionDAG
+
 [component_0]
 type = Library
 name = CodeGen