Refactor warnings and errors (#1728)

* Remove `err` and `warn`, keep `errx` and `warnx`, using them in RGBGFX too

* Separate RGBGFX and RGBLINK warnings/errors from main options

* Separate `report` function into `error` and `fatal` messages

* Implicit newlines for most RGBASM errors

include/gfx/warning.hpp

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef RGBDS_GFX_WARNING_HPP
+#define RGBDS_GFX_WARNING_HPP
+
+// Prints the error count, and exits with failure
+[[noreturn]]
+void giveUp();
+
+// If any error has been emitted thus far, calls `giveUp()`
+void requireZeroErrors();
+
+// Prints an error, and increments the error count
+[[gnu::format(printf, 1, 2)]]
+void error(char const *fmt, ...);
+
+// Prints a fatal error, increments the error count, and gives up
+[[gnu::format(printf, 1, 2), noreturn]]
+void fatal(char const *fmt, ...);
+
+#endif // RGBDS_GFX_WARNING_HPP