[WebAssembly] Add multivalue and tail-call target features

Summary:
These features will both be implemented soon, so I thought I would
save time by adding the boilerplate for both of them at the same time.

Reviewers: aheejin

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, sunfish, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D62047

llvm-svn: 361516
diff --git a/clang/lib/Basic/Targets/WebAssembly.h b/clang/lib/Basic/Targets/WebAssembly.h
index a0516da..9665156 100644
--- a/clang/lib/Basic/Targets/WebAssembly.h
+++ b/clang/lib/Basic/Targets/WebAssembly.h
@@ -36,6 +36,8 @@
   bool HasBulkMemory = false;
   bool HasAtomics = false;
   bool HasMutableGlobals = false;
+  bool HasMultivalue = false;
+  bool HasTailCall = false;
 
 public:
   explicit WebAssemblyTargetInfo(const llvm::Triple &T, const TargetOptions &)