Rename the exports variable in preamble.js to instExports (#20231)

This avoids a bug (or limitation) in Google's Closure compiler that does not
allow any variable named exports to be reassigned. Without this change, some
build configurations result in an error message like this:

[JSC_EXPORT_NOT_AT_MODULE_SCOPE] Exports must be at the top-level of a module  543|
     exports = Asyncify.instrumentWasmExports(exports);  

Since the exports variable used in the preamble is not related to Closure modules,
simply renaming the variable does the trick.

Author: KeatonTech

src/preamble.js

@@ -948,18 +948,18 @@ function createWasm() {
   // performing other necessary setup
   /** @param {WebAssembly.Module=} module*/
   function receiveInstance(instance, module) {
-    var exports = instance.exports;
+    wasmExports = instance.exports;
 
 #if RELOCATABLE
-    exports = relocateExports(exports, {{{ GLOBAL_BASE }}});
+    wasmExports = relocateExports(wasmExports, {{{ GLOBAL_BASE }}});
 #endif
 
 #if ASYNCIFY
-    exports = Asyncify.instrumentWasmExports(exports);
+    wasmExports = Asyncify.instrumentWasmExports(wasmExports);
 #endif
 
 #if ABORT_ON_WASM_EXCEPTIONS
-    exports = instrumentWasmExportsWithAbort(exports);
+    wasmExports = instrumentWasmExportsWithAbort(wasmExports);
 #endif
 
 #if MAIN_MODULE
@@ -969,7 +969,7 @@ function createWasm() {
       dynamicLibraries = metadata.neededDynlibs.concat(dynamicLibraries);
     }
 #endif
-    mergeLibSymbols(exports, 'main')
+    mergeLibSymbols(wasmExports, 'main')
 #if '$LDSO' in addedLibraryItems
     LDSO.init();
 #endif
@@ -979,10 +979,9 @@ function createWasm() {
 #endif
 
 #if MEMORY64 || CAN_ADDRESS_2GB
-    exports = applySignatureConversions(exports);
+    wasmExports = applySignatureConversions(wasmExports);
 #endif
 
-    wasmExports = exports;
     {{{ receivedSymbol('wasmExports') }}}
 
 #if PTHREADS
@@ -1039,15 +1038,15 @@ function createWasm() {
 #if !DECLARE_ASM_MODULE_EXPORTS
     // If we didn't declare the asm exports as top level enties this function
     // is in charge of programatically exporting them on the global object.
-    exportWasmSymbols(exports);
+    exportWasmSymbols(wasmExports);
 #endif
 
 #if PTHREADS || WASM_WORKERS
     // We now have the Wasm module loaded up, keep a reference to the compiled module so we can post it to the workers.
     wasmModule = module;
 #endif
     removeRunDependency('wasm-instantiate');
-    return exports;
+    return wasmExports;
   }
   // wait for the pthread pool (if any)
   addRunDependency('wasm-instantiate');