powerpc: Fix signal handling in backtrace

powerpc: Fix signal handling in backtrace

Now with read consolidation which uses SYSCALL_CANCEL macro, a frame
pointer is created in the syscall code and this makes the powerpc
backtrace obtain a bogus entry for the signal handling patch.

It is because it does not setup the correct frame pointer register
(r1) based on the saved value from the kernel sigreturn.  It was not
failing because the syscall frame pointer register was the same one
for the next frame (the function that actually called the syscall).

This patch fixes it by setup the next stack frame using the saved
one by the kernel sigreturn.  It fixes tst-backtrace{5,6} from
the read consolidation patch.

Checked on powerpc-linux-gnu and powerpc64le-linux-gnu.

	* sysdeps/powerpc/powerpc32/backtrace.c (is_sigtramp_address): Use
	void* for argument type and use VDSO_SYMBOL macro.
	(is_sigtramp_address_rt): Likewise.
	(__backtrace): Setup expected frame pointer address for signal
	handling.
	* sysdeps/powerpc/powerpc64/backtrace.c (is_sigtramp_address): Use
	void* for argumetn type and use VSDO_SYMBOL macro.
	(__backtrace): Setup expected frame pointer address for signal
	handling.