m68k: Fix sigaction kernel definition (BZ #23960)

m68k: Fix sigaction kernel definition (BZ #23960)

Commit b4a5d26d883 (linux: Consolidate sigaction implementation) added
a wrong kernel_sigaction definition for m68k, meant for __NR_sigaction
instead of __NR_rt_sigaction as used on generic Linux sigaction
implementation.  This patch fixes it by using the Linux generic
definition meant for the RT kernel ABI.

Checked the signal tests on emulated m68-linux-gnu (Aranym).  It fixes
the faulty signal/tst-sigaction and man works as expected.

	Adhemerval Zanella  <adhemerval.zanella@linaro.org>
	James Clarke  <jrtc27@jrtc27.com>

	[BZ #23960]
	* sysdeps/unix/sysv/linux/kernel_sigaction.h (HAS_SA_RESTORER):
	Define if SA_RESTORER is defined.
	(kernel_sigaction): Define sa_restorer if HAS_SA_RESTORER is defined.
	(SET_SA_RESTORER, RESET_SA_RESTORER): Define iff the macro are not
	already defined.
	* sysdeps/unix/sysv/linux/m68k/kernel_sigaction.h (SA_RESTORER,
	kernel_sigaction, SET_SA_RESTORER, RESET_SA_RESTORER): Remove
	definitions.
	(HAS_SA_RESTORER): Define.
	* sysdeps/unix/sysv/linux/sparc/kernel_sigaction.h (SA_RESTORER,
	SET_SA_RESTORER, RESET_SA_RESTORER): Remove definition.
	(HAS_SA_RESTORER): Define.
	* sysdeps/unix/sysv/linux/nios2/kernel_sigaction.h: Include generic
	kernel_sigaction after define SET_SA_RESTORER and RESET_SA_RESTORER.
	* sysdeps/unix/sysv/linux/powerpc/kernel_sigaction.h: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/sigaction.c: Likewise.