Switch llvm to overlay convention

.orchestra/config/components.yml

 #@ load("@ytt:template", "template")
 #@ load("@ytt:data", "data")
 
-#@ load("/components/llvm.lib.yml", "llvm_component")
 #@ load("/components/llvm_documentation.lib.yml", "llvm_documentation_component")
 #@ load("/components/llvmcpy.lib.yml", "llvmcpy_component")
 #@ load("/components/clang_release.lib.yml", "clang_release_component")
@@ -48,7 +47,6 @@
 
 #@ load("/global_options.lib.yml", "options")
 components:
-  llvm: #@ llvm_component
   llvm-documentation: #@ llvm_documentation_component
   llvmcpy: #@ llvmcpy_component
   clang-release: #@ clang_release_component

.orchestra/config/components/llvm.lib.yml → .orchestra/config/components/llvm.yml

+#@ load("@ytt:overlay", "overlay")
 #@ load("/lib/optimization_flavors.lib.yml", "typical_project_flavors")
 #@ load("/components/llvm_common.lib.yml", "configure_llvm")
 #@ load("/lib/fn_args.lib.yml", "mandatory")
@@ -45,5 +46,8 @@ builds:
   #@ end
 #@ end
 
+#@overlay/match by=overlay.all, expects=1
+#@overlay/match-child-defaults missing_ok=True
 ---
-#@ llvm_component = _llvm_component()
+components:
+  llvm: #@ _llvm_component()