docs: Bring TableGen syntax a bit closer to reality.

It's not just def's but actually a limited subset of Object's that are
allowed inside a multiclass.

Spotted by Joel Jones.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171935 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/TableGen/LangRef.rst b/docs/TableGen/LangRef.rst
index 34098a0..8fdf467 100644
--- a/docs/TableGen/LangRef.rst
+++ b/docs/TableGen/LangRef.rst
@@ -370,6 +370,7 @@
 
 .. productionlist::
    MultiClass: "multiclass" `TokIdentifier` [`TemplateArgList`]
-             : [":" `BaseMultiClassList`] "{" `MultiClassDef`+ "}"
+             : [":" `BaseMultiClassList`] "{" `MultiClassObject`+ "}"
    BaseMultiClassList: `MultiClassID` ("," `MultiClassID`)*
    MultiClassID: `TokIdentifier`
+   MultiClassObject: `Def` | `Defm` | `Let` | `Foreach`