meson: add note about coreutils version with ln --relative

https://bugs.freedesktop.org/show_bug.cgi?id=90799
(cherry picked from commit cd001016a166bb849c454e7b5cdb58053f34935b)

diff --git a/pwx b/pwx
index d02be29f9b5aade86aaaa6c148a51dbbb6838b55..d29aef72c627a06fa4efa79577728dd31aaf4792 160000 (submodule)
--- a/pwx
+++ b/pwx
@@ -1 +1 @@
-Subproject commit d02be29f9b5aade86aaaa6c148a51dbbb6838b55
+Subproject commit d29aef72c627a06fa4efa79577728dd31aaf4792