Fix SYSCALL_CANCEL for empty argumetns

This patch fixes the SYSCALL_CANCEL macro for usage with zero argument
number (for instance SYSCALL_CANCEL (pause)) using a similar approach
used for SOCKETCALL_CANCEL.

GLIBC build still does not hit this issue still since SYSCALL_CANCEL
is not currently being used for zero arguments calls.

Tested on i386, x86_64, powerpc64le, aarch64.

	* sysdeps/unix/sysdep.h (SYSCALL_CANCEL): Fix macro for zero argument
	syscalls.
	(__SYSCALL0): New macro.
	(__SYSCALL1): Likewise.
	(__SYSCALL2): Likewise.
	(__SYSCALL3): Likewise.
	(__SYSCALL4): Likewise.
	(__SYSCALL5): Likewise.
	(__SYSCALL6): Likewise.
	(__SYSCALL7): Likewise.
	(__SYSCALL_CONCAT_X): Likewise.
	(__SYSCALL_CONCAT): Likewise.
	(__SYSCALL_DIST): Likewise.
	(__SYSCALL_CALL): Likewise.