libbb: fix '--help' handling in FEATURE_SH_NOFORK=y

Most BusyBox applets respond to the '--help' option by printing
a usage message.  This is normally handled by busybox_main() so
applet main routines don't have support for '--help'.

In standalone shell mode with FEATURE_SH_NOFORK enabled nofork
applets are invoked directly, bypassing busybox_main().  This
results in inconsistent handling of '--help':

- applets which call getopt() report "unrecognized option '--help'"
  and print help anyway;

- realpath says "--help: No such file or directory" and doesn't
  print help;

- usleep says "invalid number '--help'" and doesn't print help.

Avoid inconsistency by checking for '--help' in run_nofork_applet().

Bug found by Ron Yorston.

function                                             old     new   delta
show_usage_if_dash_dash_help                           -      70     +70
run_nofork_applet                                    347     362     +15
run_applet_no_and_exit                               432     365     -67
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/1 up/down: 85/-67)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 135d9111d..ece03e7d8 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1219,6 +1219,7 @@ void run_noexec_applet_and_exit(int a, const char *name, char **argv) NORETURN F
 int find_applet_by_name(const char *name) FAST_FUNC;
 void run_applet_no_and_exit(int a, const char *name, char **argv) NORETURN FAST_FUNC;
 #endif
+void show_usage_if_dash_dash_help(int applet_no, char **argv) FAST_FUNC;
 #if defined(__linux__)
 void set_task_comm(const char *comm) FAST_FUNC;
 #else