Merge Emscripten downstream changes to emscripten-libs-16

Given that I started
emscripten-core/emscripten#20405 and OOO for
nearly a month and then in the meantime llvm 17.0.4 came out, I'd like
to update to not 17.0.3 but 17.0.4, with the most recent downstream
changes. These are the downstream changes happened during the last
month.

Author: aheejin

libcxx/src/new.cpp

@@ -90,10 +90,34 @@ operator new(std::size_t size) _THROW_BAD_ALLOC
     return p;
 }
 
+#if defined(__EMSCRIPTEN__) && defined(_LIBCPP_NO_EXCEPTIONS)
+void* _new_nothrow(size_t size) noexcept
+{
+    /// We cannot call ::operator new(size) here because it would abort
+    /// when malloc returns 0 and exceptions are disabled.
+    /// Expected behaviour of std::nothrow is to return 0 in that case.
+    void* p = nullptr;
+    if (size == 0)
+        size = 1;
+    while ((p = ::malloc(size)) == nullptr)
+    {
+        std::new_handler nh = std::get_new_handler();
+        if (nh)
+            nh();
+        else
+            break;
+    }
+    return p;
+}
+#endif
+
 _LIBCPP_WEAK
 void*
 operator new(size_t size, const std::nothrow_t&) noexcept
 {
+#if defined(__EMSCRIPTEN__) && defined(_LIBCPP_NO_EXCEPTIONS)
+    return _new_nothrow(size);
+#else
     void* p = nullptr;
 #ifndef _LIBCPP_NO_EXCEPTIONS
     try
@@ -107,6 +131,7 @@ operator new(size_t size, const std::nothrow_t&) noexcept
     }
 #endif // _LIBCPP_NO_EXCEPTIONS
     return p;
+#endif // __EMSCRIPTEN__ && _LIBCPP_NO_EXCEPTIONS
 }
 
 _LIBCPP_WEAK
@@ -120,6 +145,9 @@ _LIBCPP_WEAK
 void*
 operator new[](size_t size, const std::nothrow_t&) noexcept
 {
+#if defined(__EMSCRIPTEN__) && defined(_LIBCPP_NO_EXCEPTIONS)
+    return _new_nothrow(size);
+#else
     void* p = nullptr;
 #ifndef _LIBCPP_NO_EXCEPTIONS
     try
@@ -133,6 +161,7 @@ operator new[](size_t size, const std::nothrow_t&) noexcept
     }
 #endif // _LIBCPP_NO_EXCEPTIONS
     return p;
+#endif // __EMSCRIPTEN__ && _LIBCPP_NO_EXCEPTIONS
 }
 
 _LIBCPP_WEAK