From: "Randy.Dunlap" <rddunlap@osdl.org>

Add syscalls.h, which contains prototypes for the kernel's system calls.
Replace open-coded declarations all over the place.  This patch found a
couple of prior bugs.  It appears to be more important with -mregparm=3 as we
discover more asmlinkage mismatches.

Some syscalls have arch-dependent arguments, so their prototypes are in the
arch-specific unistd.h.  Maybe it should have been asm/syscalls.h, but there
were already arch-specific syscall prototypes in asm/unistd.h...

Tested on x86, ia64, x86_64, ppc64, s390 and sparc64.  May cause
trivial-to-fix build breakage on other architectures.