+/* backtrace() from <execinfo.h> is really useful, but it is not signal safe
+ * everywhere, such as on x86-64. */
+#if HAVE_EXECINFO_H && !defined __x86_64__
+# define USE_BACKTRACE 1
+# include <execinfo.h>
+#else
+# define USE_BACKTRACE 0
+#endif
+