[WebAssembly] Add version to object file metadata

Summary: See https://github.com/WebAssembly/tool-conventions/issues/54

Subscribers: jfb, dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D46069

llvm-svn: 330969
diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index 0f8a42a..0e12270 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -857,8 +857,9 @@
     const std::map<StringRef, std::vector<WasmComdatEntry>> &Comdats) {
   SectionBookkeeping Section;
   startCustomSection(Section, "linking");
-  SectionBookkeeping SubSection;
+  encodeULEB128(wasm::WasmMetadataVersion, getStream());
 
+  SectionBookkeeping SubSection;
   if (SymbolInfos.size() != 0) {
     startSection(SubSection, wasm::WASM_SYMBOL_TABLE);
     encodeULEB128(SymbolInfos.size(), getStream());