getcwd.2, mq_notify.2, mq_open.2, mq_timedreceive.2, mq_timedsend.2, mq_unlink.2: Reinstate links to section 3 pages that document system calls

Some of the links removed in commit 247c654385 should
have been kept, because in some cases there are real system
calls whose wrapper functions are documented in Section 3.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/getcwd.2

@@ -0,0 +1,2 @@
+.so man3/getcwd.3
+.\" Because getcwd(3) is layered on a system call of the same name

man2/mq_notify.2

@@ -0,0 +1,2 @@
+.so man3/mq_notify.3
+.\" Because mq_notify(3) is layered on a system call of the same name

man2/mq_open.2

@@ -0,0 +1,2 @@
+.so man3/mq_open.3
+.\" Because mq_open(3) is layered on a system call of the same name

man2/mq_timedreceive.2

@@ -0,0 +1,2 @@
+.so man3/mq_timedreceive.3
+.\" Because mq_timedreceive(3) is layered on a system call of the same name

man2/mq_timedsend.2

@@ -0,0 +1,2 @@
+.so man3/mq_timedsend.3
+.\" Because mq_timedsend(3) is layered on a system call of the same name

man2/mq_unlink.2

@@ -0,0 +1,2 @@
+.so man3/mq_unlink.3
+.\" Because mq_unlink(3) is layered on a system call of the same name