consolidate cond_syscall and SYSCALL_ALIAS declarations

take them to asm/linkage.h, with default in linux/linkage.h

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/avr32/include/asm/unistd.h

@@ -41,12 +41,4 @@
 #define __ARCH_WANT_SYS_VFORK
 #define __ARCH_WANT_SYS_CLONE
 
-/*
- * "Conditional" syscalls
- *
- * What we want is __attribute__((weak,alias("sys_ni_syscall"))),
- * but it doesn't work on all toolchains, so we just do it by hand
- */
-#define cond_syscall(x) asm(".weak\t" #x "\n\t.set\t" #x ",sys_ni_syscall");
-
 #endif /* __ASM_AVR32_UNISTD_H */