i386 Linux signal trampoline support for gdb 4.18

[Jim Blandy]

> These patches add support for the signal trampoline code used by the
> i386 Linux kernel.  These patches are against gdb 4.18.

Thanks!  I've applied this patch.

If someone wants to contribute support for RT signals or the newer
glibc trampolines, that would be great.

1999-07-29  Jim Blandy  <jimb@savonarola.red-bean.com>

	Change from Ian Lance Taylor <ian@zembu.com>.  The
	i386_linux_sigtramp* functions should be moved to
	i386-linux-tdep.c, when that file is introduced.

	* config/i386/tm-linux.h (LINUX_SIGCONTEXT_SIZE): Define.
	(LINUX_SIGCONTEXT_PC_OFFSET): Define.
	(LINUX_SIGCONTEXT_SP_OFFSET): Define.
	(SIGCONTEXT_PC_OFFSET): Don't define.
	(I386_LINUX_SIGTRAMP): Define.
	(IN_SIGTRAMP): Define.
	(i386_linux_sigtramp): Declare.
	(sigtramp_saved_pc): Define.
	(i386_linux_sigtramp_saved_pc): Declare.
	(FRAMELESS_SIGNAL): Define.
	(FRAME_CHAIN, FRAME_SAVED_PC): Define after #undef.
	* i386-tdep.c (i386_linux_sigtramp_start): New static function if
	I386_LINUX_SIGTRAMP.
	(i386_linux_sigtramp): New function if I386_LINUX_SIGTRAMP.
	(i386_linux_sigtramp_saved_pc): Likewise.
	(i386_linux_sigtramp_saved_sp): Likewise.

1999-07-29  Jim Blandy  <jimb@savonarola.red-bean.com>

	* gdb.base/signals.exp: Don't expect getting a backtrace from
	within a signal handler to fail on Linux.