gh-127503: Improve tracebacks on Emscripten when there is a trap

This PR solves two problems:
1. No Python traceback shown on segfault/trap
2. The JavaScript source line is shown

The JavaScript source line is super long and completely unenlightening,
whereas the Python traceback is very helpful.

Author: hoodmane

Tools/wasm/emscripten/node_entry.mjs

@@ -32,6 +32,8 @@ const thisProgramIndex = process.argv.findIndex((x) =>
 
 const settings = {
   preRun(Module) {
+    // Globally expose API object so we can access it if we raise on startup.
+    globalThis.Module = Module;
     mountDirectories(Module);
     Module.FS.chdir(process.cwd());
     Object.assign(Module.ENV, process.env);
@@ -45,4 +47,12 @@ const settings = {
   arguments: process.argv.slice(thisProgramIndex + 1),
 };
 
-await EmscriptenModule(settings);
+try {
+  await EmscriptenModule(settings);
+} catch(e) {
+  // Show JavaScript exception and traceback
+  console.warn(e);
+  // Show Python exception and traceback
+  Module.__Py_DumpTraceback(2, Module._PyGILState_GetThisThreadState());
+  process.exit(1);
+}

configure

@@ -2370,7 +2370,7 @@ AS_CASE([$ac_sys_system],
     dnl Include file system support
     AS_VAR_APPEND([LINKFORSHARED], [" -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js"])
     AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV"])
-    AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET"])
+    AS_VAR_APPEND([LINKFORSHARED], [" -sEXPORTED_FUNCTIONS=_main,_Py_Version,__PyRuntime,__PyEM_EMSCRIPTEN_COUNT_ARGS_OFFSET,_PyGILState_GetThisThreadState,__Py_DumpTraceback"])
     AS_VAR_APPEND([LINKFORSHARED], [" -sSTACK_SIZE=5MB"])
 
     AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [