BuildSystem: Move all userpace libraries under the userspace directory

As the number of libraries is increasing, root directory starts to
expand. This adds better organization for libraries

userspace/libraries/LibC/icxxabi.cpp

@@ -0,0 +1,41 @@
+#include <BAN/Assert.h>
+#include <stdint.h>
+#include <stddef.h>
+
+#define ATEXIT_MAX_FUNCS 128
+
+struct atexit_func_entry_t
+{
+	void(*func)(void*);
+	void* arg;
+	void* dso_handle;
+};
+
+static atexit_func_entry_t __atexit_funcs[ATEXIT_MAX_FUNCS];
+static size_t __atexit_func_count = 0;
+
+extern "C" int __cxa_atexit(void(*func)(void*), void* arg, void* dso_handle)
+{
+	if (__atexit_func_count >= ATEXIT_MAX_FUNCS)
+		return -1;
+	auto& atexit_func = __atexit_funcs[__atexit_func_count++];
+	atexit_func.func = func;
+	atexit_func.arg = arg;
+	atexit_func.dso_handle = dso_handle;
+	return 0;
+};
+
+extern "C" void __cxa_finalize(void* f)
+{
+	for (size_t i = __atexit_func_count; i > 0; i--)
+	{
+		auto& atexit_func = __atexit_funcs[i - 1];
+		if (atexit_func.func == nullptr)
+			continue;
+		if (f == nullptr || f == atexit_func.func)
+		{
+			atexit_func.func(atexit_func.arg);
+			atexit_func.func = nullptr;
+		}
+	}
+};