Windows: add pthread_sigmask() that does nothing

diff --git a/RelNotes b/RelNotes
index 540b756d2f64d8c8ebf927a707b9b2cc0a4c6151..c66ca680015d2cc4a17edb3aefab75317a6f569f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.5.txt
\ No newline at end of file
+Documentation/RelNotes/2.7.4.txt
\ No newline at end of file