tests: fix incorrect || fail pattern in tests

* tests/ls/stat-free-symlinks.sh: s/|| fail/|| fail=1/.
* tests/misc/tee.sh: Likewise.
* tests/touch/relative.sh: Likewise.
* cfg.mk (sc_prohibit_or_fail): A new syntax-check to avoid this.

cfg.mk

@@ -519,6 +519,14 @@ sc_prohibit_and_fail_1:
 	in_vc_files='^tests/'						\
 	  $(_sc_search_regexp)
 
+# Ensure that tests don't use `cmd ... || fail` as that's a noop.
+sc_prohibit_or_fail:
+	@prohibit='\|\| fail$$'						\
+	exclude=':#'							\
+	halt='|| fail detected. Please use: || fail=1'			\
+	in_vc_files='^tests/'						\
+	  $(_sc_search_regexp)
+
 # Ensure that env vars are not passed through returns_ as
 # that was seen to fail on FreeBSD /bin/sh at least
 sc_prohibit_env_returns:

tests/ls/stat-free-symlinks.sh

@@ -32,7 +32,7 @@ ln -s x link-to-x || framework_failure_
 # symlink and an executable file properly.
 
 LS_COLORS='or=0:mi=0:ex=01;32:ln=01;35' \
-  strace -qe stat ls -F --color=always x link-to-x > out.tmp 2> err || fail
+  strace -qe stat ls -F --color=always x link-to-x > out.tmp 2> err || fail=1
 # Elide info messages strace can send to stdout of the form:
 #   [ Process PID=1234 runs in 32 bit mode. ]
 sed '/Process PID=/d' out.tmp > out

tests/misc/tee.sh

@@ -37,7 +37,7 @@ done
 tee - <sample >out 2>err || fail=1
 compare sample ./- || fail=1
 compare sample out || fail=1
-compare /dev/null err || fail
+compare /dev/null err || fail=1
 
 # Ensure tee exits early if no more writable outputs
 if test -w /dev/full && test -c /dev/full; then

tests/touch/relative.sh

@@ -26,7 +26,7 @@ TZ=UTC0 touch --date='2004-01-16 12:00 +0000' f || framework_failure_
 # Set times back by 5 days.
 touch --ref f --date='-5 days' f || fail=1
 
-TZ=UTC0 ls -og --time-style=+%Y-%m-%d f > out.1 || fail
+TZ=UTC0 ls -og --time-style=+%Y-%m-%d f > out.1 || fail=1
 sed 's/ f$//;s/.* //' out.1 > out
 
 cat <<\EOF > exp || framework_failure_