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/link/patch.cpp

@@ -5,14 +5,15 @@
 #include <deque>
 #include <inttypes.h>
 #include <stdint.h>
+#include <variant>
 #include <vector>
 
+#include "diagnostics.hpp"
 #include "helpers.hpp" // assume
 #include "linkdefs.hpp"
 #include "opmath.hpp"
 #include "verbosity.hpp"
 
-#include "link/main.hpp"
 #include "link/section.hpp"
 #include "link/symbol.hpp"
 #include "link/warning.hpp"
@@ -566,7 +567,7 @@ static void applyFilePatches(Section &section, Section &dataSection) {
 
 // Applies all of a section's patches, iterating over "components" of unionized sections
 static void applyPatches(Section &section) {
-	if (!sect_HasData(section.type)) {
+	if (!sectTypeHasData(section.type)) {
 		return;
 	}