Make STARTUP_WITH_SHELL a runtime toggle -- add new "set/show startup-with-shell" option.

Occasionaly we hear about people having problems with GDB not being
able to start programs (with "run"/"start").  GDB spawns a shell to
start the program, and most often, it'll be the case that the problem
is actually with the user's shell setup.

GDB has code to disable the use of the shell to start programs.
That's the STARTUP_WITH_SHELL macro that native targets could set to 0
in their nm.h file (though no target actually uses it nowadays).

This patch makes that setting a run-time knob instead.  This will be
useful to quickly diagnose such shell issues, and might also come in
handy at other times (such as when debugging the shell itself, if you
don't have a different shell handy).

gdb/
2013-10-24  Pedro Alves  <palves@redhat.com>

	* NEWS (New options): Mention set/show startup-with-shell.
	* config/alpha/nm-osf3.h (START_INFERIOR_TRAPS_EXPECTED): Set to 2
	instead of 3.
	* fork-child.c (fork_inferior, startup_inferior): Handle 'set
	startup-with-shell'.
	(show_startup_with_shell): New function.
	(_initialize_fork_child): Register the set/show startup-with-shell
	commands.
	* inf-ptrace.c (inf_ptrace_create_inferior): Remove comment.
	* inf-ttrace.c (inf_ttrace_him): Remove comment.
	* procfs.c (procfs_init_inferior): Remove comment.
	* infcmd.c (startup_with_shell): New global.
	* inferior.h (startup_with_shell): Declare global.
	(STARTUP_WITH_SHELL): Delete.
	(START_INFERIOR_TRAPS_EXPECTED): Set to 1 by default instead of 2.

gdb/doc/
2013-10-24  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Starting): Document set/show startup-with-shell.

gdb/inferior.h

@@ -257,6 +257,25 @@ extern void notice_new_inferior (ptid_t, int, int);
 extern struct value *get_return_value (struct value *function,
                                        struct type *value_type);
 
+/* Whether to start up the debuggee under a shell.
+
+   If startup-with-shell is set, GDB's "run" will attempt to start up
+   the debuggee under a shell.
+
+   This is in order for argument-expansion to occur.  E.g.,
+
+   (gdb) run *
+
+   The "*" gets expanded by the shell into a list of files.
+
+   While this is a nice feature, it may be handy to bypass the shell
+   in some cases.  To disable this feature, do "set startup-with-shell
+   false".
+
+   The catch-exec traps expected during start-up will be one more if
+   the target is started up with a shell.  */
+extern int startup_with_shell;
+
 /* Address at which inferior stopped.  */
 
 extern CORE_ADDR stop_pc;
@@ -346,25 +365,12 @@ struct displaced_step_closure *get_displaced_step_closure_by_addr (CORE_ADDR add
 #define ON_STACK 1
 #define AT_ENTRY_POINT 4
 
-/* If STARTUP_WITH_SHELL is set, GDB's "run"
-   will attempts to start up the debugee under a shell.
-   This is in order for argument-expansion to occur.  E.g.,
-   (gdb) run *
-   The "*" gets expanded by the shell into a list of files.
-   While this is a nice feature, it turns out to interact badly
-   with some of the catch-fork/catch-exec features we have added.
-   In particular, if the shell does any fork/exec's before
-   the exec of the target program, that can confuse GDB.
-   To disable this feature, set STARTUP_WITH_SHELL to 0.
-   To enable this feature, set STARTUP_WITH_SHELL to 1.
-   The catch-exec traps expected during start-up will
-   be 1 if target is not started up with a shell, 2 if it is.
-   - RT
-   If you disable this, you need to decrement
-   START_INFERIOR_TRAPS_EXPECTED in tm.h.  */
-#define STARTUP_WITH_SHELL 1
+/* Number of traps that happen between exec'ing the shell to run an
+   inferior and when we finally get to the inferior code, not counting
+   the exec for the shell.  This is 1 on most implementations.
+   Overridden in nm.h files.  */
 #if !defined(START_INFERIOR_TRAPS_EXPECTED)
-#define START_INFERIOR_TRAPS_EXPECTED	2
+#define START_INFERIOR_TRAPS_EXPECTED	1
 #endif
 
 struct private_inferior;