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

src/fix/warning.cpp

@@ -2,6 +2,13 @@
 
 #include "fix/warning.hpp"
 
+#include <inttypes.h>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "diagnostics.hpp"
 #include "style.hpp"
 
 // clang-format off: nested initializers