Properly fix $LINENO crash on ARM (re: 23b7a163) and other bugs

The typecast fix was insufficient, avoiding the crash only when
compiling with optimisation disabled. The real problem is that
put_lineno() was passed a misaligned pointer, and that the value
didn't actually contain a double but a string. The bug occurred
when restoring the LINENO value upon exiting a virtual subshell.

Thanks to Harald van Dijk for figuring out the fix.

src/cmd/ksh93/sh/subshell.c: nv_restore():
- When restoring a special variable as defined by nv_cover(),
  do not pass either the np->nvflag bits or NV_NOFREE. Why?
  * The np->nvflag bits are not needed. They are also harmful
    because they may include the NV_INTEGER bit. This is set
    when the value is numeric. However, nv_getval() always
    returns the value in string form, converting it if it is
    numeric. So the NV_INTEGER flag should never be passed
    to nv_putval() when it uses the result of nv_getval().
  * According to nval.3, the NV_NOFREE flag stops nv_putval() from
    creating a copy of the value. But this should be unnecessary
    because the earlier _nv_unset(mp,NV_RDONLY|NV_CLONE) should
    ensure there is no previous value. In addition, the NV_NOFREE
    flag triggered another bug that caused the value of SECONDS to
    be corrupted upon restoring it when exiting a virtual subshell.
- When restoring a regular variable, copy the entire nvalue union
  and not just the 'cp' member. In practice this worked because
  no current member of the nvalue union is larger than a pointer.
  However, there is no guarantee it will stay that way.

src/cmd/ksh93/tests/leaks.sh:
- Add disabled test for a memory leak that was discovered in the
  course of dealing with this bug. The fix doesn't introduce or
  influence it. It will have to be dealt with later.

src/cmd/ksh93/tests/locale.sh:
- Add test for restoring locale on leaving virtual subshell.
  https://github.com/ksh93/ksh/issues/253#issuecomment-815290154

src/cmd/ksh93/tests/variables.sh:
- Test against corruption of SECONDS on leaving virtual subshell.
  https://github.com/ksh93/ksh/issues/253#issuecomment-815191052

Co-authored-by: Harald van Dijk <harald@gigawatt.nl>
Progresses: https://github.com/ksh93/ksh/issues/253

src/cmd/ksh93/sh/subshell.c

@@ -392,9 +392,9 @@ static void nv_restore(struct subshell *sp)
 		}
 		mp->nvflag = np->nvflag|(flags&NV_MINIMAL);
 		if(nv_cover(mp))
-			nv_putval(mp, nv_getval(np),np->nvflag|NV_NOFREE|NV_RDONLY);
+			nv_putval(mp,nv_getval(np),NV_RDONLY);
 		else
-			mp->nvalue.cp = np->nvalue.cp;
+			mp->nvalue = np->nvalue;
 		if(nofree && np->nvfun && !np->nvfun->nofree)
 			free((char*)np->nvfun);
 		np->nvfun = 0;

src/cmd/ksh93/tests/leaks.sh

@@ -439,5 +439,17 @@ after=$(getmem)
 err_exit_if_leak 'PWD and/or OLDPWD changed by cd'
 cd $original_pwd
 
+# ======
+# https://github.com/ksh93/ksh/issues/253#issuecomment-815308466
+: <<'disabled'	# TODO: known leak(s) (approx 1008 KiB after 16384 iterations)
+before=$(getmem)
+for ((i=0; i < N; i++))
+do
+	(SECONDS=1; LANG=C)
+done
+after=$(getmem)
+err_exit_if_leak 'Variable with discipline function in subshell causes memory leak'
+disabled
+
 # ======
 exit $((Errors<125?Errors:125))

src/cmd/ksh93/tests/locale.sh

@@ -349,7 +349,7 @@ x=$(LC_ALL=debug $SHELL -c 'typeset -R10 x="a<2b|>c";print -r -- "${x}"')
 x=$(LC_ALL=debug $SHELL -c 'typeset -L10 x="a<2b|>c";print -r -- "${x}"')
 [[ $x == 'a<2b|>c   ' ]] || err_exit 'typeset -L10 should end in three spaces'
 
-if	false &&  # Disable this test because it really test the OS-provided en_US.UTF-8 locale data, which may be broken.
+if	false &&  # Disable this test because it really tests the OS-provided en_US.UTF-8 locale data, which may be broken.
 	$SHELL -c "export LC_ALL=en_US.UTF-8; c=$'\342\202\254'; [[ \${#c} == 1 ]]" 2>/dev/null
 then	LC_ALL=en_US.UTF-8
 	unset i p1 p2 x
@@ -378,5 +378,18 @@ then	LC_ALL=en_US.UTF-8
 	
 fi
 
+# ======
+# The locale should be restored along with locale variables when leaving a virtual subshell.
+# https://github.com/ksh93/ksh/issues/253#issuecomment-815290154
+if	((SHOPT_MULTIBYTE))
+then
+	unset "${!LC_@}"
+	LANG=C.UTF-8
+	exp=$'5\n10\n5'
+	got=$(eval 'var=äëïöü'; echo ${#var}; (LANG=C; echo ${#var}); echo ${#var})
+	[[ $got == "$exp" ]] || err_exit "locale is not restored properly upon leaving virtual subshell" \
+		"(expected $(printf %q "$exp"); got $(printf %q "$got"))"
+fi
+
 # ======
 exit $((Errors<125?Errors:125))

src/cmd/ksh93/tests/variables.sh

@@ -1261,5 +1261,15 @@ got="$($SHELL -c 'PS4="${.sh.subshell}"; echo ${.sh.subshell}')"
 [[ "$exp" == "$got" ]] || err_exit "\${.sh.subshell} is wrongly unset in the \$PS4 prompt" \
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 
+# ======
+# Corruption of SECONDS on leaving virtual subshell
+# https://github.com/ksh93/ksh/issues/253#issuecomment-815191052
+osec=$SECONDS
+(SECONDS=20)
+nsec=$SECONDS
+if	((nsec<osec || nsec>osec+0.1))
+then	err_exit "SECONDS corrupted after leaving virtual subshell (expected $osec, got $nsec)"
+fi
+
 # ======
 exit $((Errors<125?Errors:125))