[WebAssebmly] Add Module name to WasmSymbol

[sbc100]

Summary

Imports in a wasm module can have custom module name. This change
adds the module name to the WasmSymbol structure so that the linker
can preserve this module name.

This is needed to fix: https://bugs.llvm.org/show_bug.cgi?id=37168

llvm/trunk/include/llvm/BinaryFormat/Wasm.h

struct WasmInitFunc {
   uint32_t Priority;
   uint32_t Symbol;
 };
 
 struct WasmSymbolInfo {
   StringRef Name;
   uint8_t Kind;
   uint32_t Flags;
+  StringRef Module; // For undefined symbols the module name of the import
   union {
     // For function or global symbols, the index in function or global index
     // space.
     uint32_t ElementIndex;
     // For a data symbols, the address of the data relative to segment.
     WasmDataReference DataRef;
   };
 };

llvm/trunk/lib/Object/WasmObjectFile.cpp

case wasm::WASM_SYMBOL_TYPE_FUNCTION:
         FunctionType = &Signatures[FunctionTypes[FuncIndex]];
         wasm::WasmFunction &Function = Functions[FuncIndex];
         if (Function.SymbolName.empty())
           Function.SymbolName = Info.Name;
       } else {
         wasm::WasmImport &Import = *ImportedFunctions[Info.ElementIndex];
         FunctionType = &Signatures[Import.SigIndex];
         Info.Name = Import.Field;
+        Info.Module = Import.Module;
       }
       break;
 
     case wasm::WASM_SYMBOL_TYPE_GLOBAL:
       Info.ElementIndex = readVaruint32(Ptr);
       if (!isValidGlobalIndex(Info.ElementIndex) ||
           IsDefined != isDefinedGlobalIndex(Info.ElementIndex))
         return make_error<GenericBinaryError>("invalid global symbol index",