[WebAssembly] Fixed disassembler not knowing about new brlist operand

Summary:
The previously introduced new operand type for br_table didn't have
a disassembler implementation, causing an assert.

Reviewers: dschuff, aheejin

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D56227

llvm-svn: 350366
diff --git a/llvm/utils/TableGen/WebAssemblyDisassemblerEmitter.cpp b/llvm/utils/TableGen/WebAssemblyDisassemblerEmitter.cpp
index ab78571..788f142 100644
--- a/llvm/utils/TableGen/WebAssemblyDisassemblerEmitter.cpp
+++ b/llvm/utils/TableGen/WebAssemblyDisassemblerEmitter.cpp
@@ -92,6 +92,7 @@
         // Collect operand types for storage in a shared list.
         CurOperandList.clear();
         for (auto &Op : CGI.Operands.OperandList) {
+          assert(Op.OperandType != "MCOI::OPERAND_UNKNOWN");
           CurOperandList.push_back(Op.OperandType);
         }
         // See if we already have stored this sequence before. This is not