Add __cxa_init_primary_exception to library_exception.js

llvm/llvm-project#65534 added
`__cxa_init_primary_exception` function and use it in both in
libcxxabi's `__cxa_throw` and also directly in libcxx. Because we create
exceptions in JS, we need a counterpart in JS exception library too.

Author: aheejin

src/library_exceptions.js

@@ -102,17 +102,28 @@ var LibraryExceptions = {
     }
   },
 
+  // Initialize exception info and return it.
+  __cxa_init_primary_exception__deps: ['$ExceptionInfo'],
+  __cxa_init_primary_exception: (ptr, type, destructor) => {
+#if EXCEPTION_DEBUG
+    dbg('__cxa_init_primary_exception: ' + [ptrToString(ptr), type, ptrToString(destructor)]);
+#endif
+    var info = new ExceptionInfo(ptr);
+    // Initialize ExceptionInfo content after it was allocated in __cxa_allocate_exception.
+    info.init(type, destructor);
+    var ret;
+    {{{ storeException('ret', 'ptr') }}}
+    return ret;
+  },
+
   // Here, we throw an exception after recording a couple of values that we need to remember
   // We also remember that it was the last exception thrown as we need to know that later.
-  __cxa_throw__deps: ['$ExceptionInfo', '$exceptionLast', '$uncaughtExceptionCount'],
+  __cxa_throw__deps: ['$exceptionLast', '$uncaughtExceptionCount', '__cxa_init_primary_exception'],
   __cxa_throw: (ptr, type, destructor) => {
 #if EXCEPTION_DEBUG
     dbg('__cxa_throw: ' + [ptrToString(ptr), type, ptrToString(destructor)]);
 #endif
-    var info = new ExceptionInfo(ptr);
-    // Initialize ExceptionInfo content after it was allocated in __cxa_allocate_exception.
-    info.init(type, destructor);
-    {{{ storeException('exceptionLast', 'ptr') }}}
+    exceptionLast = ___cxa_init_primary_exception(ptr, type, destructor);
     uncaughtExceptionCount++;
     {{{ makeThrow('exceptionLast') }}}
   },

src/library_sigs.js

@@ -221,6 +221,7 @@ sigs = {
   __cxa_current_primary_exception__sig: 'p',
   __cxa_end_catch__sig: 'v',
   __cxa_get_exception_ptr__sig: 'pp',
+  __cxa_init_primary_exception__sig: 'pppp',
   __cxa_rethrow__sig: 'v',
   __cxa_rethrow_primary_exception__sig: 'vp',
   __cxa_throw__sig: 'vppp',