How to use macro define for x86 and 8664 linux in c

I want to compile part of my code only on x86 and 8664 linux, but not s390 linux or others. How to use the macro define in C to achieve it? I know linux is to determine linux OS, and 386, 486 and 586 to determine CPU architecture. Is there an easy macro define to determine x86 linux and 8664 linux? Thanks