syscalls.h: use gcc alias instead of assembler aliases for syscalls

Use standard gcc __attribute__((alias(foo))) to define the syscall aliases
instead of custom assembler macros.

This is far cleaner, and also fixes my LTO kernel build.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>