Linux: Move __X32_SYSCALL_BIT out of syscalls module

Author: Julian Orth

src/unix/linux_like/linux/kernel/b64/x86_64/x32/mod.rs

@@ -1,2 +1,4 @@
+pub const __X32_SYSCALL_BIT: ::c_long = 0x40000000;
+
 mod syscalls;
 pub use self::syscalls::*;