[docs] Add link to SysV ABI document.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183341 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/CompilerWriterInfo.rst b/docs/CompilerWriterInfo.rst
index cfd353c..978cf5a 100644
--- a/docs/CompilerWriterInfo.rst
+++ b/docs/CompilerWriterInfo.rst
@@ -103,6 +103,8 @@
 ABI
 ===
 
+* `System V Application Binary Interface <http://www.sco.com/developers/gabi/latest/contents.html>`_
+
 Linux
 -----