signal.7: Note the interactions of longjmp() and non-async-signal-safe functions

See http://austingroupbugs.net/view.php?id=516#c1195.

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

man3/setjmp.3

@@ -299,7 +299,7 @@ POSIX.1-2008 Technical Corrigendum 2 adds
 .\" http://austingroupbugs.net/view.php?id=516#c1195
 .BR longjmp ()
 and
-.BR setlongjmp ()
+.BR siglongjmp ()
 to the list of async-signal-safe functions.
 However, the standard recommends avoiding the use of these functions
 from signal handlers and goes on to point out that
@@ -324,6 +324,5 @@ call to a non-async-signal-safe function and
 no non-async-signal-safe functions are called after
 returning from the initial call to
 .IR main ().
-.IR main ().
 .SH SEE ALSO
 .BR signal (7)

man7/signal.7

@@ -474,7 +474,14 @@ at some arbitrary point in the execution of the program.
 POSIX has the concept of "safe function".
 If a signal interrupts the execution of an unsafe function, and
 .I handler
-calls an unsafe function, then the behavior of the program is undefined.
+either calls an unsafe function or
+.I handler
+terminates via a call to
+.BR longjmp ()
+or
+.BR siglongjmp ()
+and the program subsequently calls an unsafe function,
+then the behavior of the program is undefined.
 
 POSIX.1-2004 (also known as POSIX.1-2001 Technical Corrigendum 2)
 requires an implementation to guarantee that the following