Print stack trace on assert() failure or when calling fatal_error()

Note: this uses the __sanitizer_print_stack_trace() function from the
AddressSanitizer runtime, so it only works when AddressSanitizer is
in use.

debug.c

@@ -0,0 +1,48 @@
+#include "debug.h"
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <syslog.h>
+
+#if defined(__SANITIZE_ADDRESS__) || HAS_FEATURE(address_sanitizer)
+#include <sanitizer/asan_interface.h>
+#define ASAN_ENABLED 1
+#endif
+
+static void
+print_stack_trace(void)
+{
+#ifdef ASAN_ENABLED
+    fputs("\nStack trace:\n", stderr);
+    __sanitizer_print_stack_trace();
+#endif
+}
+
+noreturn void
+fatal_error(const char *msg, int err)
+{
+    syslog(LOG_ERR, "%s: %s", msg, strerror(err));
+    errno = err;
+    perror(msg);
+    print_stack_trace();
+    abort();
+}
+
+noreturn void
+bug(const char *file, int line, const char *func, const char *fmt, ...)
+{
+    fprintf(stderr, "\n%s:%d: BUG in %s(): ", file, line, func);
+
+    va_list ap;
+    va_start(ap, fmt);
+    vfprintf(stderr, fmt, ap);
+    va_end(ap);
+
+    fputc('\n', stderr);
+    print_stack_trace();
+    fflush(stderr);
+    abort();
+}