Implement warning diagnostic flags for RGBFIX (#1766)

* Implement warning diagnostic flags for RGBFIX

* `-m/--mbc-type help` prints to stdout

* Support `-m list` as well as `-m help`

* Make invalid `rgbfix -l` characters a fatal error, like other invalid CLI arguments

* Refactor fix/main.cpp into multiple files

include/fix/warning.hpp

@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef RGBDS_FIX_WARNING_HPP
+#define RGBDS_FIX_WARNING_HPP
+
+#include "diagnostics.hpp"
+
+enum WarningLevel {
+	LEVEL_DEFAULT,    // Warnings that are enabled by default
+	LEVEL_ALL,        // Warnings that probably indicate an error
+	LEVEL_EVERYTHING, // Literally every warning
+};
+
+enum WarningID {
+	WARNING_MBC,        // Issues with MBC specs
+	WARNING_OVERWRITE,  // Overwriting non-zero bytes
+	WARNING_SGB,        // SGB flag conflicts with old licensee code
+	WARNING_TRUNCATION, // Truncating values to fit
+
+	NB_PLAIN_WARNINGS,
+
+	NB_WARNINGS = NB_PLAIN_WARNINGS,
+};
+
+extern Diagnostics<WarningLevel, WarningID> warnings;
+
+// Warns the user about problems that don't prevent fixing the ROM
+[[gnu::format(printf, 2, 3)]]
+void warning(WarningID id, char const *fmt, ...);
+
+// Prints an error, and increments the error count
+[[gnu::format(printf, 1, 2)]]
+void error(char const *fmt, ...);
+
+// Prints a fatal error and exits
+[[gnu::format(printf, 1, 2)]]
+void fatal(char const *fmt, ...);
+
+void resetErrors();
+uint32_t checkErrors(char const *filename);
+
+#endif // RGBDS_FIX_WARNING_HPP