regress: avoid interference from systemwide /etc/ksh.kshrc

ksh, even non-interactive, loads /etc/ksh.kshrc by default. On
some systems this can be a problem, e.g. OpenBSD, which installs a
default /etc/ksh.kshrc which is designed for its version of pdksh.

Quoth sh.1:

    On systems that support a system wide /etc/ksh.kshrc
    initialization file, if the filename generated by the expansion
    of ENV begins with /./ or ././ the system wide initialization
    file will not be executed.

src/cmd/ksh93/tests/shtests,
src/cmd/ksh93/tests/builtins.sh,
src/cmd/ksh93/tests/options.sh,
src/cmd/ksh93/tests/pty.sh:
- Instead of emptying or unsetting ENV, ensure it is exported with
  a default value of /./dev/null so we skip loading the system-wide
  profile and load an empty user profile.
- Where a specific ENV path was required for the tests, prefix it
  with '/.' so it starts with '/./'.

src/cmd/ksh93/tests/builtins.sh

@@ -638,7 +638,7 @@ then	[[ $(kill -l HUP) == "$(kill -L HUP)" ]] || err_exit 'kill -l and kill -L a
 	[[ $(kill -L) == *'9) KILL'* ]] || err_exit 'kill -L output does not contain 9) KILL'
 fi
 
-unset ENV
+export ENV=/./dev/null
 v=$($SHELL 2> /dev/null +o rc -ic $'getopts a:bc: opt --man\nprint $?')
 [[ $v == 2* ]] || err_exit 'getopts --man does not exit 2 for interactive shells'
 

src/cmd/ksh93/tests/options.sh

@@ -29,7 +29,7 @@ Command=${0##*/}
 integer Errors=0
 
 unset HISTFILE
-export LC_ALL=C ENV=
+export LC_ALL=C ENV=/./dev/null
 
 ulimit -c 0
 
@@ -109,7 +109,7 @@ else
 		err_exit '-i ignores $ENV file'
 fi
 
-export ENV=
+export ENV=/./dev/null
 if	[[ -o privileged ]]
 then
 	[[ $(print env_hit | HOME=$tmp $SHELL 2>&1) == "OK" ]] &&
@@ -424,7 +424,7 @@ got=$(
 $SHELL -c '[[ $- == *c* ]]' || err_exit 'option c not in $-'
 > $tmp/.profile
 for i in i l r s D E a b e f h k n t u v x B C G H
-do	HOME=$tmp ENV= $SHELL -$i >/dev/null 2>&1 <<- ++EOF++ || err_exit "option $i not in \$-"
+do	HOME=$tmp ENV=/./dev/null $SHELL -$i >/dev/null 2>&1 <<- ++EOF++ || err_exit "option $i not in \$-"
 	[[ \$- == *$i* ]] || exit 1
 	++EOF++
 done
@@ -433,13 +433,13 @@ integer j=0
 for i in interactive login restricted allexport notify errexit \
 	noglob trackall keyword noexec nounset verbose xtrace braceexpand \
 	noclobber globstar rc
-do	HOME=$tmp ENV= $SHELL -o $i >/dev/null 2>&1 <<- ++EOF++ || err_exit "option $i not equivalent to ${letters:j:1}"
+do	HOME=$tmp ENV=/./dev/null $SHELL -o $i >/dev/null 2>&1 <<- ++EOF++ || err_exit "option $i not equivalent to ${letters:j:1}"
 	[[ \$- == *${letters:j:1}* ]] || exit 1
 	++EOF++
 	((j++))
 done
 
-export ENV= PS1="(:$$:)"
+export ENV=/./dev/null PS1="(:$$:)"
 histfile=$tmp/history
 exp=$(HISTFILE=$histfile $SHELL -c $'function foo\n{\ncat\n}\ntype foo')
 for var in HISTSIZE HISTFILE
@@ -559,6 +559,6 @@ done
 # process source files from profiles as profile files
 print '. ./dotfile' > envfile
 print $'alias print=:\nprint foobar' > dotfile
-[[ $(ENV=$PWD/envfile $SHELL -i -c : 2>/dev/null) == foobar ]] && err_exit 'files source from profile does not process aliases correctly'
+[[ $(ENV=/.$PWD/envfile $SHELL -i -c : 2>/dev/null) == foobar ]] && err_exit 'files source from profile does not process aliases correctly'
 
 exit $((Errors<125?Errors:125))

src/cmd/ksh93/tests/pty.sh

@@ -79,7 +79,7 @@ function tst
 	done
 }
 
-export PS1=':test-!: ' PS2='> ' PS4=': ' ENV= EXINIT= HISTFILE= TERM=dumb VISUAL=vi LC_ALL=C
+export PS1=':test-!: ' PS2='> ' PS4=': ' ENV=/./dev/null EXINIT= HISTFILE= TERM=dumb VISUAL=vi LC_ALL=C
 
 if	! pty $bintrue < /dev/null
 then	err_exit pty command hangs on $bintrue -- tests skipped

src/cmd/ksh93/tests/shtests

@@ -165,7 +165,8 @@ function valxml
 	return $errors
 }
 
-unset DISPLAY ENV FIGNORE HISTFILE
+unset DISPLAY FIGNORE HISTFILE
+export ENV=/./dev/null
 trap + PIPE # unadvertized -- set SIGPIPE to SIG_DFL #
 
 integer compile=-1 posix=-1 utf8=-1