Refactor error reporting to simplify BSD-style err (#949)

src/error.c

@@ -0,0 +1,87 @@
+/*
+ * This file is part of RGBDS.
+ *
+ * Copyright (c) 2005-2021, Rich Felker and RGBDS contributors.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "error.h"
+#include "platform.h"
+
+static void vwarn(char const NONNULL(fmt), va_list ap)
+{
+	fprintf(stderr, "warning: ");
+	vfprintf(stderr, fmt, ap);
+	fputs(": ", stderr);
+	perror(NULL);
+}
+
+static void vwarnx(char const NONNULL(fmt), va_list ap)
+{
+	fprintf(stderr, "warning");
+	fputs(": ", stderr);
+	vfprintf(stderr, fmt, ap);
+	putc('\n', stderr);
+}
+
+_Noreturn static void verr(char const NONNULL(fmt), va_list ap)
+{
+	fprintf(stderr, "error: ");
+	vfprintf(stderr, fmt, ap);
+	fputs(": ", stderr);
+	fputs(strerror(errno), stderr);
+	putc('\n', stderr);
+	exit(1);
+}
+
+_Noreturn static void verrx(char const NONNULL(fmt), va_list ap)
+{
+	fprintf(stderr, "error");
+	fputs(": ", stderr);
+	vfprintf(stderr, fmt, ap);
+	putc('\n', stderr);
+	exit(1);
+}
+
+void warn(char const NONNULL(fmt), ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vwarn(fmt, ap);
+	va_end(ap);
+}
+
+void warnx(char const NONNULL(fmt), ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vwarnx(fmt, ap);
+	va_end(ap);
+}
+
+_Noreturn void err(char const NONNULL(fmt), ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	verr(fmt, ap);
+	va_end(ap);
+}
+
+_Noreturn void errx(char const NONNULL(fmt), ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	verrx(fmt, ap);
+	va_end(ap);
+}