Fix 'kill -INFO' on systems that support SIGINFO (#59)

src/cmd/ksh93/data/signals.c:
- SIGINFO was absent from the table of signals, which caused
  commands like 'kill -INFO $$' to fail even on platforms with
  SIGINFO (such as macOS and FreeBSD). Fix that by adding
  it to the signal table.

src/cmd/ksh93/tests/signal.sh:
- Add a regression tests for using SIGINFO with the kill builtin.
  The test will only be run if the external kill command supports
  SIGINFO.

NEWS

@@ -21,6 +21,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   erasable:
   https://pubs.opengroup.org/onlinepubs/9699919799/utilities/vi.html#tag_20_152_13_49
 
+- The 'kill' builtin now supports the SIGINFO signal (on operating systems
+  with support for SIGINFO).
+
 2020-07-02:
 
 - Fixed a crash that occurred if a directory named '.paths' existed in any

src/cmd/ksh93/data/signals.c

@@ -107,6 +107,9 @@ const struct shtable2 shtab_signals[] =
 #else
 	"INT",		VAL(SIGINT,SH_SIGINTERACTIVE),			"",
 #endif /* JOBS */
+#ifdef SIGINFO
+	"INFO",		VAL(SIGINFO,SH_SIGIGNORE),			S("Information request"),
+#endif	/* SIGINFO */
 #ifdef SIGIO
 	"IO",		VAL(SIGIO,SH_SIGDONE),				S("IO signal"),
 #endif	/* SIGIO */

src/cmd/ksh93/tests/signal.sh

@@ -459,5 +459,12 @@ $SHELL -c 'kill %% 2> /dev/null'; [[ $? == 1 ]] || err_exit $'`kill` doesn\'t ha
 $SHELL -c 'kill %+ 2> /dev/null'; [[ $? == 1 ]] || err_exit $'`kill` doesn\'t handle a non-existent job correctly when passed \'%+\''
 $SHELL -c 'kill %- 2> /dev/null'; [[ $? == 1 ]] || err_exit $'`kill` doesn\'t handle a non-existent job correctly when passed \'%-\''
 
+# ======
+# SIGINFO should be supported by the kill builtin on platforms that have it.
+if "$(whence -p kill)" -INFO $$ 2> /dev/null
+then
+	kill -INFO $$ || err_exit '`kill` cannot send SIGINFO to processes when passed `-INFO`'
+fi
+
 # ======
 exit $((Errors<125?Errors:125))