Linux: Use system call tables during build

Linux: Use system call tables during build

Use <arch-syscall.h> instead of <asm/unistd.h> to obtain the system
call numbers.  A few direct includes of <asm/unistd.h> need to be
removed (if the system call numbers are already provided indirectly
by <sysdep.h>) or replaced with <sys/syscall.h>.

Current Linux headers for alpha define the required system call names,
so most of the _NR_* hacks are no longer needed.  For the 32-bit arm
architecture, eliminate the INTERNAL_SYSCALL_ARM macro, now that we
have regular system call names for cacheflush and set_tls.  There are
more such cleanup opportunities for other architectures, but these
cleanups are required to avoid macro redefinition errors during the
build.

For ia64, it is desirable to use <asm/break.h> directly to obtain
the break number for system calls (which is not a system call number
itself).  This requires replacing __BREAK_SYSCALL with
__IA64_BREAK_SYSCALL because the former is defined as an alias in
<asm/unistd.h>, but not in <asm/break.h>.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>