Some refactoring and cleanup (#1806)

* Use clang-tidy `misc-include-cleaner` for IWYU `#include` cleanup

* Use `std::optional<size_t>` instead of `ssize_t`

* Rename some functions in linkdefs.hpp

* Fix header order

include/asm/output.hpp

@@ -6,7 +6,6 @@
 #include <memory>
 #include <stdint.h>
 #include <string>
-#include <unordered_map>
 #include <vector>
 
 #include "linkdefs.hpp"