Fix anachronism/typo in syntax of declaration of llvm.va_start.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190552 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/LangRef.rst b/docs/LangRef.rst
index 98654f3..f961188 100644
--- a/docs/LangRef.rst
+++ b/docs/LangRef.rst
@@ -6310,7 +6310,7 @@
 
 ::
 
-      declare void %llvm.va_start(i8* <arglist>)
+      declare void @llvm.va_start(i8* <arglist>)
 
 Overview:
 """""""""