[WebAssembly] Add an LLVM_FALLTHROUGH to address a warning. NFC.

llvm-svn: 324777
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
index 7e284ea..59bf1ad 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
@@ -1165,6 +1165,7 @@
   switch (getSimpleType(Store->getValueOperand()->getType())) {
   case MVT::i1:
     VTIsi1 = true;
+    LLVM_FALLTHROUGH;
   case MVT::i8:
     Opc = WebAssembly::STORE8_I32;
     break;