No more globals.hh in headers

This is needed to rearrange include order, but I also think it is a good
thing anyways, as we seek to reduce the use of global settings variables
over time.

src/libstore/store-api.cc

@@ -27,6 +27,11 @@ using json = nlohmann::json;
 
 namespace nix {
 
+Path StoreConfigBase::getDefaultNixStoreDir()
+{
+    return settings.nixStore;
+}
+
 StoreConfig::StoreConfig(const Params & params)
     : StoreConfigBase(params)
     , StoreDirConfig{storeDir_}