Remove libcxx stub library and move operator new to mammoth.

lib/mammoth/src/new.cpp

@@ -0,0 +1,7 @@
+#include <stdint.h>
+#include <stdlib.h>
+
+[[nodiscard]] void* operator new(uint64_t size) { return malloc(size); }
+[[nodiscard]] void* operator new[](uint64_t size) { return malloc(size); }
+
+void operator delete(void*, uint64_t) {}