Stop the time keyword overriding errexit (#351)

This bug was first reported in <https://www.illumos.org/issues/7694>.
The time keyword currently overrides the errexit shell option,
allowing failing scripts to continue after an error:

  $ cat 1.sh
  #!/bin/sh
  time false   # This should cause the script to exit
  echo FAILURE
  true
  $ ksh -o errexit 1.sh

  real    0m0.00s
  user    0m0.00s
  sys     0m0.00s
  FAILURE

src/cmd/ksh93/sh/xec.c:
- When the time keyword runs a command, pass the errexit state flag
  to the sh_exec call. This state flag is required for ksh to exit
  when a command fails while the errexit option is on.

src/cmd/ksh93/tests/basic.sh:
- Add a regression test based on the reproducer.

NEWS

@@ -3,6 +3,11 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-11-29:
+
+- A bug that caused the time keyword to override the errexit shell option has
+  been fixed.
+
 2021-11-24:
 
 - The --posix mode was amended to stop the '.' command (but not 'source') from