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

src/gfx/warning.cpp

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: MIT
+
+#include "gfx/warning.hpp"
+
+#include <limits>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static uintmax_t nbErrors;
+
+[[noreturn]]
+void giveUp() {
+	fprintf(stderr, "Conversion aborted after %ju error%s\n", nbErrors, nbErrors == 1 ? "" : "s");
+	exit(1);
+}
+
+void requireZeroErrors() {
+	if (nbErrors != 0) {
+		giveUp();
+	}
+}
+
+void error(char const *fmt, ...) {
+	va_list ap;
+	fputs("error: ", stderr);
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	putc('\n', stderr);
+
+	if (nbErrors != std::numeric_limits<decltype(nbErrors)>::max()) {
+		nbErrors++;
+	}
+}
+
+[[noreturn]]
+void fatal(char const *fmt, ...) {
+	va_list ap;
+	fputs("FATAL: ", stderr);
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	putc('\n', stderr);
+
+	if (nbErrors != std::numeric_limits<decltype(nbErrors)>::max()) {
+		nbErrors++;
+	}
+
+	giveUp();
+}