sh: Keep ignored SIGINT/SIGQUIT after set in a background job

If job control is not enabled, a background job (... &) ignores SIGINT and
SIGQUIT, but this can be reverted using the trap builtin in the same shell
environment.

Using the set builtin to change options would also revert SIGINT and SIGQUIT
to their previous dispositions.

This broke due to r317298. Calling setsignal() reverts the effect of
ignoresig().

Reported by:	bdrewery
MFC after:	1 week

bin/sh/main.c

@@ -134,6 +134,7 @@ main(int argc, char *argv[])
 	setstackmark(&smark);
 	setstackmark(&smark2);
 	procargs(argc, argv);
+	trap_init();
 	pwd_init(iflag);
 	INTON;
 	if (iflag)

bin/sh/tests/execution/Makefile

@@ -19,6 +19,7 @@ ${PACKAGE}FILES+=		bg9.0
 ${PACKAGE}FILES+=		bg10.0 bg10.0.stdout
 ${PACKAGE}FILES+=		bg11.0
 ${PACKAGE}FILES+=		bg12.0
+${PACKAGE}FILES+=		bg13.0
 ${PACKAGE}FILES+=		env1.0
 ${PACKAGE}FILES+=		fork1.0
 ${PACKAGE}FILES+=		fork2.0

bin/sh/tests/execution/bg13.0

@@ -0,0 +1,16 @@
+# $FreeBSD$
+
+T=`mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXXXX`
+trap 'rm -rf $T' 0
+cd $T || exit 3
+mkfifo fifo1
+# Use a trap, not the default action, since the shell may catch SIGINT and
+# therefore its processing may be delayed.
+{ set -C; trap 'exit 5' TERM; read dummy <fifo1; exit 4; } &
+exec 3>fifo1
+kill -INT "$!"
+kill -TERM "$!"
+exec 3>&-
+wait "$!"
+r=$?
+[ "$r" = 5 ]

bin/sh/trap.c

@@ -474,14 +474,20 @@ dotrap(void)
 }
 
 
+void
+trap_init(void)
+{
+	setsignal(SIGINT);
+	setsignal(SIGQUIT);
+}
+
+
 /*
  * Controls whether the shell is interactive or not based on iflag.
  */
 void
 setinteractive(void)
 {
-	setsignal(SIGINT);
-	setsignal(SIGQUIT);
 	setsignal(SIGTERM);
 }
 

bin/sh/trap.h

@@ -45,6 +45,7 @@ void ignoresig(int);
 int issigchldtrapped(void);
 void onsig(int);
 void dotrap(void);
+void trap_init(void);
 void setinteractive(void);
 void exitshell(int) __dead2;
 void exitshell_savedstatus(void) __dead2;