Make fixes and improvements

- Document more compiler flags
- Expose new __print_maps() api
- Better overflow checking in mmap()
- Improve the shell example somewhat
- Fix minor runtime bugs regarding stacks
- Make kill() on fork()+execve()'d children work
- Support CLONE_CHILD_CLEARTID for proper joining
- Fix recent possible deadlock regression with --ftrace

libc/runtime/printargs.greg.c

@@ -337,7 +337,7 @@ textstartup void __printargs(const char *prologue) {
 
   PRINT("");
   PRINT("MEMTRACK");
-  PrintMemoryIntervals(2, &_mmi);
+  __print_maps();
 
   PRINT("");
   PRINT("TERMIOS");