Windows: add pthread_sigmask() that does nothing

diff --git a/RelNotes b/RelNotes
index 8ee12bf8a31a83289e4be3b0bbba88b5775ac7c9..c66ca680015d2cc4a17edb3aefab75317a6f569f 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/1.7.12.2.txt
\ No newline at end of file
+Documentation/RelNotes/2.7.4.txt
\ No newline at end of file