[wasm] Allow to build browser in library mode

src/tasks/WasmAppBuilder/PInvokeTableGenerator.cs

@@ -386,11 +386,12 @@ private void EmitNativeToInterp(StreamWriter w, List<PInvokeCallback> callbacks)
             sb.Append(") { \n");
             if (!is_void)
                 sb.Append($"  {MapType(method.ReturnType)} res;\n");
-
+#if TARGET_WASI
             if (_isLibraryMode && HasAttribute(method, "System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute"))
             {
                 sb.Append($"  initialize_runtime(); \n");
             }
+#endif
 
             // In case when null force interpreter to initialize the pointers
             sb.Append($"  if (!(WasmInterpEntrySig_{cb_index})wasm_native_to_interp_ftndescs [{cb_index}].func) {{\n");

src/tools/illink/src/ILLink.Tasks/build/Microsoft.NET.ILLink.targets

@@ -140,6 +140,11 @@ Copyright (c) .NET Foundation. All rights reserved.
     </PropertyGroup>
 
     <Delete Files="@(_LinkedResolvedFileToPublishCandidate)" />
+    <ItemGroup>
+      <TrimmerRootAssembly Condition="'$(RuntimeIdentifier)' == 'browser-wasm' And '%(Identity)' == '@(IntermediateAssembly)' And '$(OutputType)' == 'Library'">
+        <RootMode>all</RootMode>
+      </TrimmerRootAssembly>
+    </ItemGroup>
     <ILLink AssemblyPaths="@(ManagedAssemblyToLink)"
             ReferenceAssemblyPaths="@(ReferencePath)"
             RootAssemblyNames="@(TrimmerRootAssembly)"