Add example for auto debugging and asm() usage

ape/ape.S

@@ -1932,4 +1932,4 @@ __data_start:
 	.hidden	__piro_start
 
 .end
-
+

examples/auto-launch-gdb-on-crash.c

@@ -0,0 +1,44 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/log/log.h"
+
+/**
+ * Automatically launchs GDB Debugger TUI during crash.
+ *
+ * Run the following inside a terminal:
+ *
+ *     sudo apt install gdb
+ *     make -j12 o//examples/auto-launch-gdb-on-crash.com
+ *     o//examples/auto-launch-gdb-on-crash.com
+ *
+ * Backtrace is logged instead if run outside interactive terminal.
+ * Environmental factors such as GDB, MAKEFLAGS, ADDR2LINE, TERM, and
+ * isatty(STDERR_FILENO) should also be taken into consideration:
+ *
+ *     $ export GDB=eoatuhshtuone
+ *     $ o//examples/auto-launch-gdb-on-crash.com
+ *     error: Uncaught SIGTRAP
+ *     etc. etc.
+ *
+ * @see https://www.felixcloutier.com/x86/intn:into:int3:int1
+ * @see https://en.wikipedia.org/wiki/INT_(x86_instruction)#INT3
+ * @see examples and reference material on using the asm() keyword
+ *     - libc/nexgen32e/bsf.h
+ *     - libc/nexgen32e/tzcnt.h
+ *     - libc/nexgen32e/cpuid4.h
+ *     - libc/nexgen32e/tinystrcmp.h
+ *     - https://gist.github.com/jart/fe8d104ef93149b5ba9b72912820282c
+ */
+
+int main(int argc, char *argv[]) {
+  showcrashreports();
+  asm("int3"); /* cf. die(), perror("msg"), abort(), exit(1), _Exit(1) */
+  return 0;
+}