Address non-determinism in DWARF

see https://github.com/rust-lang/llvm-project/pull/20/commits/c263ee986fc90d8413f444ced7610dfbdfe97be6#r344425408
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
index 419f217..9fbf4bb 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyMachineFunctionInfo.h
@@ -61,7 +61,7 @@
 
 public:
   explicit WebAssemblyFunctionInfo(MachineFunction &MF)
-      : MF(MF), SPVReg(WebAssembly::NoRegister) {}
+      : MF(MF), SPVReg(WebAssembly::NoRegister), SPLocal(-1) {}
   ~WebAssemblyFunctionInfo() override;
   void initializeBaseYamlFields(const yaml::WebAssemblyFunctionInfo &YamlMFI);