Switch host toolchain components to overlay convention

.orchestra/config/components.yml

 #@ load("@ytt:template", "template")
 #@ load("@ytt:data", "data")
 
-#@ load("/components/toolchain/arch/host.lib.yml", "host_toolchain_components")
 #@ load("/components/toolchain/arch/x86_64.lib.yml", "x86_64_toolchain_components")
 #@ load("/components/toolchain/arch/i386.lib.yml", "i386_toolchain_components")
 #@ load("/components/toolchain/arch/arm.lib.yml", "arm_toolchain_components")
@@ -16,7 +15,6 @@
 
 #@ load("/global_options.lib.yml", "options")
 components:
-  _: #@ template.replace(host_toolchain_components)
   _: #@ template.replace(x86_64_toolchain_components)
   _: #@ template.replace(i386_toolchain_components)
   _: #@ template.replace(arm_toolchain_components)

.orchestra/config/components/toolchain/arch/host.lib.yml → .orchestra/config/components/toolchain/arch/host.yml

+#@ load("@ytt:overlay", "overlay")
 #@ load("/components/toolchain/lib/toolchain.lib.yml", "create_toolchain_components")
 #@ load("/components/toolchain/lib/common.lib.yml", "linker_flags")
 
@@ -44,6 +45,7 @@ extra_binutils_configure_options:
 extra_gcc_make_variables: LIBRARY_PATH=/usr/lib/x86_64-linux-gnu
 #@ end
 
+#@overlay/match by=overlay.all, expects=1
+#@overlay/match-child-defaults missing_ok=True
 ---
-
-#@ host_toolchain_components = create_toolchain_components(**_params())
+components: #@ create_toolchain_components(**_params())