AK: Provide a fallback definition for std::nothrow

AK/kmalloc.cpp

@@ -60,4 +60,10 @@ void operator delete[](void* ptr, size_t) noexcept
     return free(ptr);
 }
 
+// This is usually provided by libstdc++ in most cases, and the kernel has its own definition in
+// Kernel/Heap/kmalloc.cpp. If neither of those apply, the following should suffice to not fail during linking.
+namespace AK_REPLACED_STD_NAMESPACE {
+const nothrow_t nothrow;
+}
+
 #endif