[RS6000] libgcc cfi

[RS6000] libgcc cfi

There are a few places in libgcc assembly where we don't emit call
frame information for functions, potentially breaking unwinding from
asynchronous signal handlers.  This patch fixes them.  Although I
patch tramp.S there is no attempt made to provide CFI for the actual
trampoline on the stack.  Doing that would require generating CFI at
run time and both registering and deregistering it, which is probably
not worth doing since it would significantly slow down the call.

	* config/rs6000/morestack.S (__stack_split_initialize),
	(__morestack_get_guard, __morestack_set_guard),
	(__morestack_make_guard): Provide CFI covering these functions.
	* config/rs6000/tramp.S (__trampoline_setup): Likewise.

From-SVN: r266503