make require_stdlib fast path wait on package_locks

Author: IanButterworth

base/loading.jl

@@ -2507,6 +2507,9 @@ function require_stdlib(uuidkey::PkgId, ext::Union{Nothing, String}=nothing)
         uuidkey = PkgId(uuid5(uuidkey.uuid, ext), ext)
     end
     if root_module_exists(uuidkey)
+        lock = get(package_locks, uuidkey, nothing)
+        # must wait as require_lock is released around package __init__s
+        lock !== nothing && wait(lock[2])
         return loaded_modules[uuidkey]
     end
     # first since this is a stdlib, try to look there directly first