[TableGen] Don't use inline storage for ReferenceLocs (NFC)

The ReferenceLocs are not enabled by default (they are used by the
tablegen lsp server), and as such always empty, but still allocate
inline storage for the SmallVector. Disabling it saves about 200MB
on RISCVGenGlobalISel.inc.

(The equivalent field in Record already disables inline storage.)

Author: nikic

llvm/include/llvm/TableGen/Record.h

@@ -1523,7 +1523,7 @@ class RecordVal {
   bool IsUsed = false;
 
   /// Reference locations to this record value.
-  SmallVector<SMRange> ReferenceLocs;
+  SmallVector<SMRange, 0> ReferenceLocs;
 
 public:
   RecordVal(const Init *N, const RecTy *T, FieldKind K);